For me personally, I purposefully avoid checking for feedback for a given period of time, like a day, a week etc, depending on the work. I also try to make stuff that I want to see myself, rather than trying to make stuff I think other people want to see. If I like it, chances are there are other people that like it. Audiences can often tell when something is made with passion rather than made specifically for mass appeal.

As for the reaching out to popular groups stuff, here's the thing. I've been in groups of popular artists in fandoms before, and we can usually tell when people are reaching out in good faith and when people are reaching out specifically because we're popular and they want in on that kind of group. You say that you're reaching out just to get to know them, but clearly it's more than that, since you've said yourself that you feel jealous and competitive, and you're aiming for these popular people and groups because they're popular. Whenever I end up in one of those groups it's usually entirely by chance because some of my art got relatively popular in that fandom, enough to be shared a little bit, which resulted in more visibility, which lead to natural engagement with people who saw my stuff. If people saw my stuff and followed me, and I saw their stuff and followed them, as mutuals we saw more of each other, started commenting on each other's works, worked on the same group projects, joined the same discord groups, made fanart for each other, etc. It came about naturally, not because we sought out popular groups specifically. I've also been in groups of not as popular artists in smaller fandoms, and the process was similar if not the same. The only difference was scope.

And I've been in the position where people regularly reached out to me because of my popularity and I can tell that they've only done so because I was popular in that fandom and they wanted some attention from someone popular. It's usually pretty easy to tell, and it just makes me feel awkward. I communicate with groups of artist friends I've made because we found we had a lot in common and got to know each other and enjoyed talking to each other. People who come at me without building a rapport first are likely to get either awkward, brief replies, or no reply at all, depending on how they open. And you'd be surprised at how many people try contacting you out of the blue when you're popular in a decently sized fandom, often trying to get me to look at their art, or read something they wrote, or give critique, or promote their stuff, and so on (I don't like to share/reblog/retweet/etc something someone sends me unless I would have anyway, so that puts me on the spot as well). So if I had to guess, chances are these people you reached out to aren't responding for the same reason I sometimes don't want to respond, because it can be a bit tiring to filter through all those messages and people vying for attention, especially when you get the vibe that they're only contacting you because you're popular. I was more willing to engage with people who were sincere and shared my interests and just wanted to have a chill conversation because they saw stuff I posted and had stuff to say about the topic, or characters, or meta, etc. But if I got the vibe that they wanted something from me or that contacting me was something strategic for their own gain, then I was less likely to respond. I don't mind giving the occasional advice, but I don't want to be on the receiving end of someone else's self promotion. I was more likely to check out the works of someone I vibed with who didn't push me to look at their stuff (sharing specific works that were relevant to an ongoing topic of conversation is fine, that's more organic, but most people weren't sharing their stuff for that reason)

It might help to go into this thinking of it as a community effort, with everyone on the same team, rather than seeing it as a leaderboard. Works you put out are there for the sake of enriching the fandom, keeping it alive, providing diverse content, and fleshing out the community.

Try to get into the habit of posting stuff without looking at how many likes or shares or comments you get, at least not right away. Also, try posting more low effort stuff. Do some lazy doodles sometimes. They're just as important to a fandom ecosystem as high effort works. Not everything you put out has to be something you pour all of your need for validation into. Heck, make some art that you don't intend to post, or at least wait to post stuff until a while has passed. Other things you can try is purposefully posting at non-strategic times when you're less likely to get noticed, draw stuff that you want to draw even if you think that other people won't like it. Etc. You need to desensitize yourself to the concept of failing, or "losing".

Even if you can't get rid of that competitive mindset, you can at least try to be less of a sore loser. I've been there, so I get it, that need for validation. It's addictive. What worked for me was forcing myself to become okay with "losing" on purpose. I purposefully avoided seeking out validation for an extended period. When you eliminate it as a factor, you relearn how to operate without it as a driving force. You might stop making stuff for a while at first if it's a really strong factor for you, but if you have the drive of an artist that got you creating to begin with, then eventually you'll develop an itch you need to scratch by drawing. And when you do, just post it without thinking about it, the moment it's finished. Doesn't matter if it's an opportune time or not, just do it, don't think about it.

And then let it go. Don't check for notifications about it, don't check for comments, go about your day as if you never posted at all. Post your next work without checking for feedback on the first. Just do that for a little while, before you consider going back to check for feedback on the earlier ones. Get used to creating without knowing or wanting to know what people think about it. Become desensitized to the thought of throwing your work out into the void and knowing you may never get an answer back. And try to make just as much indulgent lazy content as you do high effort content, don't filter yourself.

In my experience over time it becomes a habit to create stuff without taking an audience into consideration, which helps to balance your desires and expectations. After a while you can go back to looking at feedback, but do so casually. Don't count how many interactions you get, just glance over to get a general idea of what people think. Don't think about it in terms of numbers. Look at the individuals. There's 1000 times more value in one heartfelt comment from someone who was genuinely touched by something you made, than there is in thousands of mindless voiceless button presses from thousands of faceless accounts. And tbh I've found that I get a better response as a result. People often respond to sincere passion if you let yourself make stuff that you enjoy just because you enjoy it and not because you crave validation. Some of my most popular works are shitposts or experiments or super indulgent pieces that I made for myself and no one else.

But you have to be willing to put in the time and effort to break free of the unhealthy habits you've built up and reframe your way of thinking about fandom communities and how you engage with them. If you want to reach out to someone do it because you have something you want to say to them related to the interests they've showcased in their works, not because you just want a relationship with someone popular because they're popular and you want to be popular too. And reach out to people whether they're popular or not. Connections aren't all forged from the top down after all, many of the people in those popular groups became popular because they sought out like-minded people to begin with, and their small group grew over time.

This got longer than I initially intended, but TL;DR: if you want to care less about "winning" all the time, make a habit out of losing on purpose.