Is it possibly a network issue, which just happens to coincide with the software update? They are not always consistent with their signals. It can happen. I'm just saying that because I've the the A53 as a one of my spare phones. I always check if they operate as expected after a system software update. Mine seems exactly the same as normal.
I presume if you received the update via OTA, then your device is stock and not rooted.
Try booting to safe mode and see if you can connect. I suspect you've got a 3rd party app or customisation that's interfering with the normal operation of your device. A UI update will not break mobile data functionality.
I have started in safe mode. No network connection. Complete reset of phone, no network connection. Diagnostic of came back normal, but not connected to a network. Diagnostic of the mobile network says it works. Sim card works in other handsets. This happened immediately after installing the update.
Where are you based? Is the phone a stock UK device, or has it been rooted / flashed? You say you've done a reset, does that include a full factory reset? Do you not find it unusual that it's only affecting a small number of users. I know other owners of this handset and they have no problems at all. If after everything the device is still not connecting to network then consider having it looked at by a Samsung technician. I believe you've already been given advice on how to do this.
