HI @forere can you try a soft Reset, hold the power Button on the Smart remote for around 5 seconds until the Samsung logo appears. If this does not make much difference try unplugging from the mains around 5 minutes. know you have difficulty accessing menu but are you able to update via USB if do not have the 1310.1 update https://www.samsung.com/uk/support/model/UE55MU6199UXZG/
See some more information here https://www.samsung.com//support/answer/ANS00062957/#:~:text=Discharging%20or%20cold%20booting%20you...
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 4.0,Android 12 Official Version.
No, it does not work.....it doesn't matter how i try to update, i get the message "Update Failed". I also noticed, it does not save any setting like Network settings.
I connect a LAN cable, after saying connect, and later it says no network connection when i try to do "Update Now"
I think the Motherboard is bad.