I just published a F-Droid repo to host the Grin++ apk officially. To add it to your F-Droid client, scan the QR code or use this URL:
https://fdroid.grinplusplus.com/fdroid/repo
If you would like to manually verify the fingerprint (SHA-256) of the repository signing key, here it is:
CB 47 7A 5C 47 62 B4 9D 0C 55 C6 58 B1 AB AF 9C 89 09 D2 A8 29 52 A3 93 FF D5 B5 BB CF 8E 99 83
EDIT: The repo stats are disabled and will remain disabled, so the repo is not tracking installs or anything like that.