Afaik there are only two options:

• App
• Chip card

Since your employer opted out of the chip card you don't have any alternatives to the app. Have you talked to your employer? I feel like this is the part of the chain which you can influence the easiest. Have you asked why they opted for the non chip solution?

There are two places in Mainz which provide the chip cards.. But one of them is part of the authorities you already contacted.. so I don't know if this will provide any new info.

So far, I've seen mixed results with using other apps besides Google Wallet.

"Back in my day", you'd just get send a pkpass file by mail or get a link to a pkpass file and you were done. Nowadays, you usually find those "add to Google wallet" links, which send you to Google, so that they can insert that file serverside into you account and the Google wallet app just displays them, after downloading them from you account.

I haven't really looked into that, but maybe take a closer look at that link? Somehow, Google need to get the data to display in the app, so it's probably either

1. The PTA sends all data for those passes preemptively to Google, whether you use it or not and only sends google an ID to that pass (that'd be a GDPR nightmare, but then, we're talking big tech...)
2. The PTA is registered with google and that link only tells google to ask their server for that data using an ID that is passed in that URL (proprietary, but fine from a GDPR perspective)
3. The link either contains all data necessary for that pass (unlikely - can contain images etc) or just contains an (encoded) link a pkpass file

In the third option, you might be able to download that pkpass yourself or craft your own file? Check every parameter and - if it looks like random combination of letters and numbers, try to decode them using base64-web (not standard Base64!)