That's up to the service to decide on the appropriate level of security risk in whether they allow unknown builds. They already don't allow custom builds on any other mobile OS, so this is really the best you can get as a user. What is your proposed solution?
> They already don't allow custom builds on any other mobile OS ...
Keep in mind that Pinephones and similar are a thing. Lots of people are hoping they don't fizzle out and die off like previous "open" phone projects. :)
And Pinephones and similar don't have apps for these services that require attestation and never will. If some allow web access without build attestation, that works on custom Android builds as well.
