@nierga8, I had this issue when I wanted to import the Just Flight Hawk-T1. I was able to get the aircraft to display in MSFS 2024 but again was only getting the tablet to say activation failed, and limited functionality with the aircraft. The way I managed to get the activation to work was to copy the licence from MSFS2020 (MS Store location, Obviously Steam is likely slightly different)
AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalState\packages\justflight-aircraft-hawk-t1
over into MSFS 2024
AppData\Local\Packages\Microsoft.Limitless_8wekyb3d8bbwe\LocalState\WASM\MSFS2020
For some reason it seems that the licences are located in a slightly different place for MSFS 24. Once I had moved the whole file over into that location, the tablet wasn’t displaying activation failed anymore, and after a few minutes left to load on the runway, I was able to operate the aircraft as I normally would in MSFS 2020. While this isn’t a perfect solution, but it’s worked for me for the Hawk-T1 at least, I do have the Vulcan as well but that only displays the cockpit in MSFS 2024. However, as per the Just Flight information, I’m sure they will crack on and get all their aircraft working in the new sim soon enough im sure. Hopefully this helps abit if you give it another attempt.