Signal doesn't have payment data. It's not a paid service.
Proton is a paid subscription service and that payment data needs to be accessible in order to charge the user and they're not a payment processor.
Not sure, they do seem to store something (pretty unclear what though), but I'm guessing that can be fully decoupled from a user's account, since it's unrelated to the actual service.
This comparison makes no sense.
Signal doesn't have payment data. It's not a paid service. Proton is a paid subscription service and that payment data needs to be accessible in order to charge the user and they're not a payment processor.
What if a user donates to Signal?
Not sure, they do seem to store something (pretty unclear what though), but I'm guessing that can be fully decoupled from a user's account, since it's unrelated to the actual service.