My ethernet connection does not work periodically I recently upgrader to BigSur ver 11.2.3

Shutdown the computer.

Turn off router. Unplug it from the wall.

Disconnect it from the computer.

Startup in Safe mode. https://support.apple.com/en-gb/HT201262

To leave Safe Mode, click  in the menu bar and choose “Restart”

Reset  SMC:   How to reset the SMC of your Mac - Apple Support   Choose the appropriate method.

Connect the router/modem to computer.

Power it on.

Test.

my friend, Big Sure doesn't respond well to third party devices (not apple). After the update, the hub from the Ugreen company stopped working altogether. The problem was solved with new patches from Ugreen, but Big Sure did not want to install these patches, despite the fact that this company is a registered developer, we had to solve this radically and completely disable the protection of my Mac. This can be done safely through the console. Or contact Apple Support for help. They will help you quickly enough. But such a decision that we came to in this case, Apple does not welcome and everything is done at your own peril and risk, as the computer becomes vulnerable to unlicensed software.

stylianos2021 wrote:

My WiFi works fine however when I turned my WiFi Off and enable my Belking USB-C adaptor periodically the online light on my router goes off and therefore my internet drops now it does it very ofthen then I will have to restart my router.