I may need/benefit from using Slack for “work stuff”.

Yeah, sucks totally, but network effect is a thing.

What is the best way to use it, on Android and on Linux, from people that use it often.

Do they have a webapp? How do they do their servers, is it centralized? Any wrappers for anything I should think of?

Using it in the work profile (GrapheneOS), getting the APK from APKpure is the option I would consider as last resort.