vintprox

Disabled presence can be an advantage to some privacy-conscious users, so a case for matrix.org can be made for them - especially if they don’t chat much anyway.

Otherwise depend on what is called a “non-puppeting bridge”, self-hosted bot that reposts messages on behalf of itself. Problem is, reactions and other multi-agent interactions won’t be a subject for bridging. If you absolutely need those, you have to host a Matrix server (like optimized, but unstable, Conduit or the hungry Synapse) or partner up with another server owner to activate your appservice…

A lot. Of. Downtimes…

If you want to make a set of private rooms that you want to be available at all times, I certainly don’t recommend matrix.org.