I downloaded FossWallet off F-Droid last week for an annual pass I bought. It only supports Apple Passkey files, but if they offer Google Wallet they'll usually offer that too.

Are you 100% sure there is no physical card? Did you ask the local provider? I just ask, because I have a physical card for the Deutschland Ticket.

Other than that there is a Deutschland Ticket app. But it won't work for every provider. It does not for mine.

https://play.google.com/store/apps/details?id=de.deutschlandticket.app

im not a proton shill, but they have a wallet. wouldnt any paid secure wallet option work? and yeah, i wouldnt trust google either