Thanks to you guys, especially @muttonhead411, I was able to get my 7490 working with OC 0.6.4 and Big Sur 11.1!
Initially, I had gestures and mouse movement working with the trackpad, but tap-click was not working for me (was not showing up as a TrackPad in System Preferences). However, after following this other post,
I fixed the tap-click, so now it all seems to work (except the trackpad buttons).
https://osxlatitude.com/forums/topic/14316-dell-7480-alps-trackpad-not-working-in-big-sur/
I've attached my EFI folder here in case it's useful to anyone (I had to take IntelBluetoothFirmware out because of size limitations on this post, and also remember to add your serial and SystemUUID under PlatformInfo).
EFI.zip