sirfartsalot I'm not sure if the following will solve your issue, but thought I'd share anyway as I went down a rabbit hole a while ago trying to get my YubiKey to work (via NFC) with the KeePassDX (password manager) mobile app. On my GrapheneOS device I do not have Google Play services installed and it works like a charm...
I managed to find this project:
https://gitlab.com/kunzisoft/android-hardware-key-driver
Project description:
Key Driver is a driver application for hardware keys (SoloKey and Yubikey) that provides an answer to a challenge for applications requiring physical key authentication.
The application allows to use :
- The hmac-secret FIDO2 functionnality of SoloKey.
- The HMAC-SHA1 challenge-response functionality of Yubikey with USB OTG or NFC connection.
The Key Driver app is available on Google Play, or via direct APK downloaded from GitLab:
https://gitlab.com/kunzisoft/android-hardware-key-driver/-/releases
Direct download:
https://gitlab.com/kunzisoft/android-hardware-key-driver/-/jobs/6788429195/artifacts/file/app/build/outputs/apk/debug/app-debug.apk
Note: the APK downloaded from GitLab has the file name app-debug.apk
but it is actually not a debug build (which is good!), and I believe it was named this way because of the fixes pushed in this version by the developer ("Fix debug mode for gitlab package")
The Key Driver app does not require any permissions (and doesn't even request them), which is also great!
Give it a try, and I hope this help!