trashpanda1 if the store says the app isn't compatible it is likely they have enabled the Play Integrity tag for their Play Store listing, some app devs do this despite their app not being PI restricted. Some are though but may still operate depending on the level they set it to in the app.
Try installing from Aurora store (only recommended for such cases as required, probably best to not use the service but individual requirements differ). If the app works fine complain to them about mislabelling/tagging their listing and add in that you'd like them to look at and implement https://grapheneos.org/articles/attestation-compatibility-guide if they are looking to secure their app.