That is not really the same, Signal is a donation and Proton is a subscription where a monthly (or yearly) request has to go to the payment provider for your fee, for this you need to keep the payment information on file and linked to the account. Signal can say I got donated by someone but they do not need to keep this information linked to a specific user, just the payment record (that still has your cc/bank details on it) for tax purposes.
That is not really the same, Signal is a donation and Proton is a subscription where a monthly (or yearly) request has to go to the payment provider for your fee, for this you need to keep the payment information on file and linked to the account. Signal can say I got donated by someone but they do not need to keep this information linked to a specific user, just the payment record (that still has your cc/bank details on it) for tax purposes.