What causes an account to get banned, like how bad does it need to be to get permanently banned

Last year, I had a permanent ban that lasted over 7 months before I was unbanned all because I had the name of a social media in one of my comments.

It depends on the severity of the rulebreak, and your past history (as in, if you've broken rules before, severely or not).
Note that the filter for instance cannot ban you irregardless of the modal that shows up - That's just telling you that if you get muted more, the ST will be notified of your behaviour and they'll view your mute log.

NoUsername-King wrote:

Last year, I had a permanent ban that lasted over 7 months before I was unbanned all because I had the name of a social media in one of my comments.

You likely had other punishments before prior to this and knowingly bypassed the comment filter.

Sites with DMing are a huge no-go, same for 13+ sites.
Only exceptions are GitHub & YouTube, as I recall - Even with those, the content you are linking mustn't have anything that breaks a rule (aka, is Scratch appropriate, if you will).

dog138 wrote:

What causes an account to get banned, like how bad does it need to be to get permanently banned

If your account is temporary, you have to wait for your acc to be restored. You will get a permanent ban when someone access teacher acc features if he/she isn't an actual teacher, or violate the Community Guidelines multiple times, etc