Hello Angus Long,
Thank you for posting in Microsoft Community forum.
Did you install RSAT tool on one domain Windows 11 Pro 23H2 client machine and open the AD Users and Computers?
Please check if you can open AD users and computers on domain controller? If so, please uninstall RSAT tool and reinstall it and check if it helps.
I hope the information above is helpful.
If you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou