My research says that your new WiFi adapter needs an RTL8812AU Linux driver, and milhouse currently includes that driver into LE.
Chances are, the driver hasn't been included into LE's major release, yet, but maybe it's already available as test build. Activate test builds (a.k.a. milhouse builds) this way:
- go to Settings -> LibreELEC -> Updates
- click Show Custom Channels
- click - Custom Channel 1
- insert http://milhouse.libreelec.tv/builds/master/RPi4 and click OK
- click Update Channel
- click Milhouse-9.80
- click Available Versions
- click the first entry at the list of test builds (not the highest number)
- confirm the update
Hopefully this update will make your driver available, and the WiFi adapter should work without any further configuration.
Good luck!
unfortunately I don't see the option, "show Custom Channels". My updates have these options, auto update, submit stats, show update notifications and the under that I have Raspberry Pi Flashing with two updates "bootloader EEPOM" and "VIA USB3 Firmware". I'm on 9.2.1. the install is only a few days old. but it wouldn't be a great loss if I had to wipe and refresh.