My internet connection stops working.

To begin, this is the 2nd computer I've had this to happen on. My connection starts up ok, but after 2 to 3 hours (sometimes even longer), the connection stops working. I check the connection, and I'm told I am connected to the internet, but the connection may be slow.

I have to perform a "network reset" in "Advanced Network Settings" & allow the PC to restart to get good connection again.

The crazy thing about this is all other devices on my LAN keep working just file at full speed. I also have a 3rd PC ( a Dell laptop) that does NOT have this problem.

Has anyone else encountered this problem? I did not have this issue until Windows 11.

Is this a wired, or wireless connection?

Both, Wired and wireless fail.

First thing, have you had a Windows Update occur recently. If so, that very likely changed something (never fails to disappoint).

Next we need a better diagnosis. When you say "the connection stops working", but also say "I'm told I am connected to the internet",
that does not compute. How do you know connection stops working? You can't get on the internet using a browser?
Have you tried a different browser?
How are you told you're connected? Are you seeing the internet icon in the task bar?
If you're looking at a statement on the Settings page, I would not trust that (Windows can get confused).
Can you open a command windows, ping www.google.com and get a response?

Other things to check:
Check the power settings and power savings for the network adapter.
Go to Device Manager > Network Adapters > right-click and select Properties > Power Management tab.
Uncheck allow computer to turn off adapter.
Next go to Power Options (via Settings or Control Panel) > Change plan settings > change advanced settings.
Go through ALL entries and see if there are any "power savings" features and disable them.
Next, log into your router as admin and look for similar power savings (e.g. Eco) features and turn them off.
Also on the router, typically under LAN settings, check that the DHCP lease time didn't get reduced. It's often set to 24 hours.

P.S. You'll probably get advice here to update your network drivers. DO NOT do that. Drivers don't go bad overnight or they don't intermittently go bad. The only way your drivers were corrupted would be if a Windows Update did that, and in that case they'll either work or not work.

If Fast Startup is enabled, disable it.

Could it be a syncing issue if you have more than one computer switched on at the same time and have Windows Backup syncing turned on? I had something like this once but only on Windows 10. The Windows 11 computers were fine. Network kept cutting out, asking me to re enter the network code again - it would last a bit then cut out again. Tried all the re-setting network settings etc. I only resolved it by using a local account instead of a microsoft account, then it was fine!