Connected to router but disconnected from internet

Try resetting the SMC and NVRAM. Also, Big Sur is still buggy, so if you have a large amount of work to do or anything that's quite demanding, I'd recommend staying on macOS Catalina for a little while.

Hey again!

In that case, can you create a new network location, (Make sure to hit Apply)? Then test?

How to use network locations:

https://support.apple.com/en-us/HT202480

This step just takes a minute and worth a try.

And, although I know your network is working fine with all other devices, which would seem to indicate a Mac issue, trust me, I’ve seen this step fix your problem many times, this should force the modem/router to re-connect to your Mac properly:

Disconnect your modem/router from power for a minute or two, re-connect it, wait for internet to establish itself again, and test again, or restart and test.

If that does fail:

I’m thinking a corrupt/old Keychain entry related to your network, testing in a new admin account, and it working just fine, may lend credence to this theory, (If you do this, I’d skip the Apple ID sign in, as to make sure the local Keychain is the only player on the field and not iCloud Keychain, but if it works fine, can then sign into iCloud and enable keychain and test). If it works fine, it’s probably the user keychain.

You can find Keychain Access, (If you haven’t been there before), in Finder > Go > Utilities.

I, personally, if the new network location didn’t resolve it, considering it DOES connect in the first place, I’d search Keychain Access for:

Airport

Network Name

ISP Name

Computer Name (As found in System Preferences > Sharing), if there.

And delete all entries, then Restart, of course you’d have to re-enter any network related passwords again, typically just once.

Hey Hondo!

My first guesses would be to:

1) In System Preferences > Network.

On the left column are the network interfaces.

If you have any referencing a VPN or any type of network filtering software such as Net Nanny, Little Snitch, Webroot, etc. I’d highlight it and press the “-“ to remove it.

Then, I’d check, in that same location Advanced > Proxies.

If anything other than the bottom most proxy configuration is enabled, uncheck it, hit Done, then Apply to apply the changes, restart and test.

Likewise, in System Preferences, do you have a category called “Profiles”? If so and it’s something you didn’t install yourself, I’d remove it in the same fashion as the network interface from earlier.

Finally, do you also see any such software in Users and Groups > Login Items? If so, I’d remove the same way then restart.

I have some other things in mind, just let me know how that goes when you can, good luck!