I looked at the community list in programming.dev (from https://programming.dev/communities) sorted by active users per month and noted down the instances for the top 100 communities
its using google sheets
going to recount with lemm.ees community list in a sec since theyre federated with hexbear
The easiest way would be subscribing to the communities you want and then using the subscribed feed instead of the all feed
Some frontends (mostly the apps) have filters you can use to filter content but the main frontend doesn’t currently apart from blocking the communities
An alternate thing to do could be to use the local feed in the instance that primarily has the content you want. Isnt doable for all types of content since not everything has a topic based instance for it and would require having a new account if you want to interact but theres things such as mander.xyz for science, programming.dev for programming/hardware/etc. topics, etc.