Set up Mastodon (same username as here) in a site-specific browser via Epichrome/Chrome apps. I believe I have come up with a way to prevent Chrome from auto-updating. This is important because v54 of Chrome breaks Epichrome SSBs. I found a Terminal script that's alleged to work but it just plain will NOT prevent Chrome from updating itself.
My cure was to install an older version of Chrome somewhere other than the Applications folder.