you can simply mutate the url from https://other.instance/c/community to https://your.instance/c/community@other.instace but yeah, it's a pain. It's a good opportunity for a simple browser extension or script that does some URL rewriting.

I found that on mobile, Jerboa has some instance url associations for major instances and that means that links can open in that, where you're logged in to your account on your home instance, and it handles it. but it's been hit-and-miss for me as to whether it'll open in the app or continue in mobile browser.