I ended up keeping chrome just for work, and using firefox for personal life.
Then I grabbed Browser Tamer and set up an AHK v2 script that, when I click on and focus any browser window, it executes browser tamer's CLI to update the default browser. Thus I get the behavior of "open links in last used browser", which is the correct browser for whatever link I click 99.9% of the time.
My solution is: The system has a default browser that opens default links. On my work machine I have a different browser where I am for example logged in to my private github account I just never want to open a clicked link there anyway. Copy/pasting 2 times per day is fine.
Edit: found it: it's hidden behind the browser.profiles.enabled setting in about:config
My work profile is logged into my work Gmail + AWS
Personal profile has my personal Google account.
The two won't mix.
The only real cost is that running things this way eats more memory, but I've not experienced OOM issues for years away from deliberately small VMs (for testing or small sever tasks) that turned out to be too small.