Iirc there was a way to set tag weight somewhere, but I can't find a way to do that now. How I can do that?

Iirc there was a way to set tag weight somewhere, but I can't find a way to do that now. How I can do that?

Somewhat related, but is there a way to exclude tags? Topics I never want to see?

AFAIK, no. You can follow a tag and set its weight to -999 for example, but that will just put the tag to the end of your feed.
It's in dev.to/dashboard/following :-)