systemctl stop kodi
nano /storage/.kodi/userdata/guisettings.xml
find and edit videoscreen.screenmode to contain <setting id="videoscreen.screenmode">0192001080060.00000pstd</setting>
find and remove any content in videoscreen.whitelist, e.g. should look like <setting id="videoscreen.whitelist"></setting>
save and exit
reboot
As long as the device presents 1080p@60 modes, it should now be the desktop resolution. This should all be selectable in the GUI anyway.. but without debug logs and such there's no way to guess why not.