It might not be forever. I had an admin shadowban me once across the entire site for daring to post on r/indiegaming and r/gaming, two subs I commented on constantly, a single link to a video game I made over six months (well at least that's the best reason I can come up with, I was never told a reason why, I know certain subreddits are super anti-self-promotion for some reason though). I didn't even notice for six months until a moderator PM'ed me and told me he had been manually approving my posts for months in one sub (the rest of the subreddits I posted to I just thought I had suddenly stopped being interesting to people).
I tried to appeal the shadowban and heard nothing from the admins.
Anyway I stayed away from Reddit for a while but eventually created a new account to talk about board games. A few years later I decided to check my other account again, and discovered it wasn't shadowbanned anymore (you can tell by going to your user page in incognito mode, it won't show up like other accounts do if it's shadowbanned). And so now I'm using that old account again.
Although I'll never talk about anything I've ever made on that site ever again, which seems kind of stupid to me, but whatever. Reddit's rules are crap (and new UI, I only use old.reddit), but I do enjoy checking and commenting in a few of the subreddits still.