Michael - it's all about software versions for all three units (GNS480, Trig TT22 and TC20 control head, if that's the transponder you're looking at using).
The issue in the past has been that Garmin did not provide the GNS480 with its proprietary "ADSB+" data format. Garmin then released version 2.4 software, purported to be the last release ever to be made for the GNS480, specifically to add "ADSB+" data output capability to the 480.
While Garmin didn't provide ADSB+ from the 480, Trig had no reason to accept the ADSB+ format. Once Garmin made the ADSB+ data format available from its GPS navigators, Trig had to reverse-engineer the data format in order to make their transponders compatible. Version 2.7 software for the TT22 accomplishes this goal. Version 1.12 is required for the TC20 control head, if used.
I have this combination in my aircraft so I can confirm all three of these software versions are available for installation.
Keep in mind that we don't need to have an STC-approved installation in our amateur-built aircraft, and since we can't ever be eligible for the $500 ADSB equipage rebate because we're Canucks, that approved list of devices to which you refer likewise doesn't apply.