Having high-end phones like Samsung Galaxy Note 20 or Note 20 Ultra does not guarantee that the devices will not fall victim to any issues. The devices have faced issues in the past, and one of the most common problems is the No Sim Card Detected error. Whether the device is not detecting a sim card or throwing errors like No Service or No signal detected, we’ve listed some fixes to eliminate those issues.
In most cases, the sim card-related errors like No Sim Card Detected, No Service, etc., can be easily fixed. But, sometimes, the problem occurs when the sim card is damaged or there’s some network issue in your area. In any case, it’s worth applying the fixes that we have listed below.

Here’s what to do if your Samsung Galaxy Note 20/Note 20 Ultra is not detecting SIM card
Fix 1: Turn Airplane Mode on and off
Whenever you face any sim card or network-related issues, you should first turn on the Airplane Mode and then turn it off. This method does the trick most of the time. This method disconnects your device from the wireless system until the option is not turned on.
None of these worked for my Note 20 Ultra