One of the newly introduced features in macOS 15 Sequoia is the ability to use private Wi-Fi addresses aka “MAC address randomisation”. https://support.apple.com/en-us/102509 By default the new setting has been changed to 'Rotating' and unfortunately this does currently pose a problem when connecting to Wi-Fi networks such as eduroam.
Any newly built macOS Sequoia 15 devices
*Note Any devices that have updated to Sequoia with existing eduroam connection settings will be unaffected.
The Private Wi-Fi Address feature offers these settings, which you can change at any time if you have administrative functionality:
Choose Apple menu > System Settings, then click Wi-Fi in the sidebar.
Click the Details button or More Info button next to the network name eduroam.
From the menu next to Private Wi-Fi Address, choose Off
Enter credentials and join network