Whack-a-mole sadly, but I will say that not every user on an instance you don’t want to interact with is necessarily going to be promoting content that you find objectionable.

Perfect! I’ll edit my post.

So the Tankie Triad is:

• lemmy.ml
• hexbear
• lemmygrad.ml

Edit: The trouble is that, as far as I know, there’s currently no way as a user to block an entire instance. You can play whack-a-/C and block communities as you bump into them. The other option is to look for instances that have de-federated from these instances, and make a new account on one of those instances.

As @Samskara@sh.itjust.works pointed out, instance blocking is possible:

You can block instances in your settings. For your instance, that’s lemmy.ca/settings then selects blocks and add the instances you want to block

Are there other servers which amplify problematic content?

There’s a lot more than the 3 listed above, the ones I listed are militant in their belief that Russia and China are Marxist-Leninist utopias. There’s some communities and users across all the instances that are problematic. If you see something you don’t like, block the user or community.