Not exactly the same thing, but the xone (XBox One controller driver for Linux) project disabled Issues on Github and uses a Discord server instead. Which is stupid as heck, because I'm not going to join a Discord server just to check if someone has already encountered the same issue as me.

It's generally nothing big enough to have heard of unless you're looking into whatever niche it fills.

Only example that comes to mind is mechanical keyboard stuff. For some of the smaller / one-off designs there was a habit of "if you need troubleshooting, here's a discord link" instead of even minimal documentation. For "standard" stuff that used the same lil microcontrollers as everything else just a minor annoyance, but saw it with ones that used custom / no microcontroller too, where even a "you need X diodes, Y sprockets, etc" would've been nice.

Like OP tend to see it and move on and forget about it because it's not worth it. The few times I really wanted to get some service running on a raspberry pi or arduino or whatever and tried the discord was a handful of 'regulars' swapping memes that were annoyed I wasn't intimately aware of their codebase.

I've only got anecdotal stories but I have heard from my friends that ROM hack projects do this and I personally don't get it. If it’s to hide from the big N, Discord won’t back you there. Just teach your users how to use patch files instead.

TrueCharts (third party app repository for TrueNAS) does this and it drove me crazy until I eventually gave up and moved everything to Docker. Lack of serious documentation was just one of the many reasons.