i have the same issue with with s21 ultra after update of one ui 6.1 . it complete broke the network. use different sim cards with different network it does not work even same sim cards with other handset perfectly working fine . did all the settings for reset and all still does not work .
Just for the clarification nothing problem with network provider it is with samsung software as i travelled to different continent and its the same issue with their sim cards and same sim cards are working on other handsets . so it does problem with samsung software. we must need the immediate resolutions. @samsungsupport team look this matter urgently .
