Can't log in on new device, because account is google, not email

I'm trying to upgrade from Classic (paid) to Locus 4, at the same time as I set up a new phone with GrapheneOS. (Old phone with Classic was standard Android.) I downloaded and installed the APK from Locus' google drive, but I cannot log in to my account because I used a google account on the old device, and without google services, no log in options are shown except "email".

Am I just stuck? I wanted to purchase a Locus 4 voucher in the store, using the offer for Classic customers. But it looks like if you originally used a google account for Locus, the only option is to create a new account and lose everything you purchased previously.

I did try the expert "use play services" toggle. No effect.

Is there any way to convert my old Locus account into an "email" type account so I don't have to start from scratch (and miss out on the one-year-free offer)?