Since you are already on Mastodon, I would start by checking out the instances of people you have interacted with. Many topic-instances are still pretty general-purpose. Decentralize yourself! Join two or three instances. Subscribe to different topics on each. See what sticks.

On a small instance, the local feed is much more important. Local users have a larger influence on what you discover. So, check the local feed first. It may be a bit boring but should be free of spam. Check the external feed. It should not be too tacky, and have a CW where you want one. Check the moderation policy. If you want to commit to only one small instance, find out who pays the hosting and maybe donate.