See if the following thread helps:
https://learn.microsoft.com/en-us/answers/questions/52687/association-file-gpo-not-working
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Hi.
I have a problem with file association via GPO in Windows 11 22H2.
When I use this procedure my default apps don't change but I export the file association with the command dism.exe /online /get-defaultappassociations and show correct association that i have configure in GPO.
Thank you.
Solution:
I have made the defaultassociations file again with the ProgID corresponding to the W11 Apps. It works fine with the GPO.
See if the following thread helps:
https://learn.microsoft.com/en-us/answers/questions/52687/association-file-gpo-not-working