Wi-Fi connected but no internet on MacBook Air after Tahoe 26.0.1 update

Does the MacBook Air work as expected when connected from another Wi-Fi network? Can you describe your network? How many Wi-Fi routers do you have? One (that possibly part of a mesh), or more than one Wi-Fi router?

Check for Wi-Fi router firmware updates, apply as available, and restart the Wi-Fi router.

If you have any Safari extensions installed, temporary disable those and test again.

Do you have a network content filter active and running in your router?

Any add-on anti-malware apps or cleaning or security apps installed, or add-on content filters?

Note: I will here assume that “I don’t have any VPN either” means no add-on VPN app is installed, and not that no VPN app is currently active. VPNs don’t need to be active to cause problems with network routing. If you have an app, follow the vendor’s instructions and remove it, restart, and test again.

One possible workaround to this issue is to create a new Network Location. In System Settings > Network, click the ••• / down caret at the bottom of the preference pane, then select Locations > Edit locations. Click the (+) button, give the location a name (you can delete it or rename it later), and see if that corrects the issue.

Turn off the firewall, Mac's and any third part firewall you might have installed.

Also can go through the list of everything you have tried.

I would try a SafeBoot Start up your Mac in safe mode - Apple Support will sort many anomalies

Login and test. Reboot as normal and test. Caches get rebuilt automatically if you haven't already.

this Apple article contains MANY suggestions:

If your device has network connectivity issues, ...