Hi @JWadle47,
I've tested the Grammarly Keyboard on my own device and it appears it doesn't support Autofill, which other keyboards such as Gboard and Microsoft Swiftkey do support.
With that said, when a keyboard doesn't support the display of autofill suggestions, autofill suggestions should appear below login fields instead. If autofill suggestions aren't appearing below login fields when the login fields have been tapped when you have Grammarly Keyboard enabled, please let us know and we'll be happy to look into this further.
I hope this helps.