I think there are no good, solid answers, and as long as you have empathy and are not intentionally getting things wrong, I think you're fine. However, some people get hung up on terms more than others, depending on their life experiences.

I know a trans man, and he says it's fine if we call him by his deadname or his old pronouns. I know it's not, but he's saying because we knew him then, it's forgivable. I personally could never. I have slipped, but I always catch myself, and I haven't slipped in a while. I'm older, I'm trying to get with the times. Not that trans people are exactly new, but acceptance of them is, and it should have been there all along.

I read something on Lemmy (not sure what instance/comm) and they said that being female (trans or cis) is defined by presentation of feminine traits, not masculine ones, and vice versa. I think if we game that statement out to its logical conclusion, then everyone is a little genderfluid as most of us do things that are feminine or masculine, but we don't identify as such, and as self-determination is also important, it's important to respect a person's chosen pronouns and/or labels.

There was a debate in another place on Lemmy over a user's pronouns being capitalised. Now here I can see some friction: in religion, a god's pronouns are also capitalised, so if someone is religious, that could be an issue. However, most of us had no problem capitalising pronouns. The issue I had was that if you slipped and forgot, they said you were anti-trans (not They as in the person, but the people who made the thread). I guess they were trying to cover their bases and asses, but I felt like that was a bridge too far. Still, I'm pretty sure I capitalised everything correctly.

So, it seems there are a lot of terms, a lot of pronouns, a lot of rules, and some of them seem like they contradict one another. But one rule I like to keep coming back to is Xbox's take on the golden rule. That is, treat others, not how you want to be treated (that being the golden rule), but how they want to be treated. We have a pronouns field on Lemmy, so it's easy to see what to call a person. If they don't specify, I refer to them by username, or OP/TC (TC is a lesser used term from forums, it means Topic Creator... OP could be a different person if you were in a comment chain and you were referring to the person who replied to the TC but started a tangent conversation... but mostly the two are interchangeable).

TL;DR: Find what works for the person you're talking to and go from there. And if they correct you on something, don't take it personally, because they've chosen to not take what they perceived as a slight, and took it instead as a chance to correct you to keep the conversation civil. Which often begs the question of conservative and older folks (the latter does include my generation), is it too much sometimes? Well, if you meet someone from another country, there are often rules you have to follow to not dishonour their culture, and you do it — it's the same with anyone. That is, if you wish to be seen as a person who is respectful of others. If not... well... do your thing, I guess. But those who are LGBTQ+ have struggles and they don't want others to have any more than they need to, and allies (of which I include myself) try to be mindful of the needs of the individual.