No idea honestly. My best guess would be that browse.feddit.de hasn't cached those communities yet if you just recently created them. There's options to turn on/off different instances in the sidebar, and it looks like feddit.de is on by default.

I think the main solution is to have an easy way of searching for existing communities before deciding to make you own. browse.feddit.de seems to be a good step in that direction to me.

After just getting started learning to do my own car maintenance, definitely the subreddit dedicated to my model of car

People have been joking lately about productivity suddenly increasing as a result of the Reddit blackout, but honestly? That loss of information is probably going to result in a loss of productivity in some cases.

Because yeah, in the nightmare scenario where both Reddit and Stack Overflow were to disappear, a lot of programmers would be at a complete loss.