If one of your accounts gets banned from a subreddit, even for a stupid reason like "because we don't like a certain other subreddit, and you commented there once", or "because we're /r/ThanosDidNothingWrong and decided to randomly ban 50% of all accounts just for fun", if you ever visit that subreddit with another account, then Reddit permanently site-bans all of your accounts.
Good to know. Is there any way to ban yourself or do you need to keep a list.
Once you get banned from a subreddit, using those multiple accounts becomes “ban evasion”. Permanent ban from all of Reddit will follow quickly after.