Or Newpipe for Android which you simply install.

You can report to mods, or to reddit itself.

I never reported violence but reported a fair deal of racism on non-english subreddits I browse. They were taken down.

Couldnt you just copy the list of instances lemmy.world or a similarly large instance federates with (its in the footer), or grab a the list of Lemmy instances from e.g fedidb.org to block?

I feel that would block most of the network, and doubt there would be much value left in joining whatever unconnected instances left.