Enter Switch Mode first
Hold Y + Home until the remote connects and the LED between Home and Screenshot turns solid blue.
Guide
Use this guide if you want custom remapping for MODI inside desktop Anki. Put the remote in Switch Mode first, then install the MODI plugin with code 406900239.
The plugin setup goes with Switch Mode, not Keyboard Mode.
Tools → Add-ons → Get Add-ons → paste 406900239 → restart Anki → open MODI Anki Remote.
Setup
This is a short setup once the remote is in the right mode.
Hold Y + Home until the remote connects and the LED between Home and Screenshot turns solid blue.
In desktop Anki, open Tools → Add-ons → Get Add-ons, paste 406900239, and restart Anki when prompted.
After Anki restarts, go back to the menu bar and open MODI Anki Remote so you can custom-remap the buttons and test them in review.
Notes
A lot of people can just review in Keyboard Mode without installing anything extra. The MODI plugin is the Switch Mode option for when you want custom remapping in Anki.