Realme Android 11:
Open Settings on right top menu and change Modes from User mode to Developer mode.
Go back -> Mobile Networks and start recording
Switch your device to Airplane Mode, wait few second and turn Airplane mode off. Wait some time to get connected to 4G LTE network.
Stop logging with stop icon / close device log
Enter to the file manager and find the log file
Android 11 and newer log file saved to File Manager -> Android -> com.coloros.logkit (To access directory open AOSP Files app via Android Settings -> Storage -> Files). Find log file log file with extension .bin (Example file name: diag_qdss_log_mpss_20210326_1734181616794458624.bin).