MuPDF comes by default on CalyxOS, and is what I use.

I don’t think it would be unreasonable to boycott all modern games until the industry seriously changes

I have MicroG

Have you tried Molly FOSS, or are you using the standard one with proprietary dependencies? Is there a meaningful difference in day to day functionality?

It should be opt-in if they want to maintain their reputation while introducing telemetry.