Hello, please see my post here:
https://discussions.apple.com/thread/250713004
Please try to reboot your MacBook into Safe Mode (holding the shift key on boot). If the Captive Portal appears it is likely a 3rd party application that is interfering with the Network Stack.
When you reload you PC back into Normal Mode you should be connected, however that doesn't necessarily mean it is fixed. This is because you have just gone through the captive portal process i.e. Accept T&Cs in Safe Mode for that day. Then after a certain period the Captive Portal may expire your session. you will need to complete the Captive Portal process again and hence it will no longer work.
So the real fix is check for applications installed that could interfere with the Network Stack such as a VPN client i.e. Cisco VPN Client or even possibly an Anti-Virus Scanner.