I think it's an F-Droid version feature that's missing, then. I just updated to v0.94.3-FDROID, & the signer option stilldoesn't exist when creating a new profile. I wonder if it's since F-Droid apps typically don't interact with Google servers for push notifications. Maybe it was considered not worth it to add the feature since it wouldn't work well without push notifications.

But Amethyst does offer push notifications thru Unified Push, so maybe there's another reason why.

Oh well. Thanks for the help, tho