Mine is a Pixel running GrapheneOS, and it doesn’t seem to be on your list. My issue is that I’m not using Google Play Services, so I don’t get the benefits that it provides, one of which is managing notifications. So Signal has to manage notifications itself, which means it basically needs to always be running instead of the more typical Android model of being woken up when there’s a notification.

Or maybe it’s what you linked. Either way, I’d check that and see if it’s an easy fix.