I am experiencing the same behavior with Windows 11 24h2 and Remote Desktop connection to Windows Server 2012 R2.
I found this work around in another thread and this works for me.
I made a folder c:\windows.old\23h2
in that folder I have two additional folders
c:\windows.old\23h2\System32
with files: mstsc.exe and mstscax.dll
c:\windows.old\23h2\System32\en-US
with files: mstc.exe.mui and mstscax.dll.mui
c:\windows.old\23h2\SystemResources
with files: mstsc.exe.mun and mstscax.dll.mum
I still had another Windows 11 pc with version 23h2, that I copied the files from.
Here's a required structure:
Just copy those dirs and files from old build of Windows 11 23H2 to some place and then make a shortcut for this mstsc.exe file to your desktop and use it for rdp connections instead of a new one from 24H2.
If you have another locale than en-US, e.g. uk-UA, copy it with corresponding files too.