@kwk_kwk I don’t know if you would find it useful to set up a whitelist of supported resolutions? The main advantage of that in this context is that it would allow you to switch output resolution on the fly during playback; so if it doesn’t select the best resolution automatically, you can change it manually.
This is not going to enable any new modes but if (as Graham says) 1080p/50 is the best mode to use, you may need to select that manually, and manually selecting modes requires a whitelist to be set up.
You can read about whitelists here: [HowTo] Guide to the Kodi whitelist function and related settings