Hi Ayşe,
Some users have experienced the same issue with Microsoft Remote Desktop not working after the macOS Big Sur update. Here are a few steps that helped me resolve the problem:
Update Microsoft Remote Desktop:
Make sure you have the latest version of Microsoft Remote Desktop from the Mac App Store. Sometimes, updates can fix compatibility issues.
Reset Microsoft Remote Desktop Preferences:
Open Finder.
Go to ~/Library/Containers/com.microsoft.rdc.mac.
Delete the folder com.microsoft.rdc.mac.
Grant Full Disk Access:
Go to System Preferences > Security & Privacy > Privacy tab.
Select Full Disk Access from the left panel.
Click the lock to make changes and add Microsoft Remote Desktop to the list.
Check Network Settings:
Ensure that your Mac's network settings haven't changed after the update.
Verify that your VPN or firewall settings aren't blocking the remote desktop connection.
Reinstall Microsoft Remote Desktop:
Uninstall the current Microsoft Remote Desktop app.
Download and install the latest version from the Mac App Store.
If these steps don't resolve the issue, you might want to check for any known compatibility issues on Microsoft's support page.
Hope this helps!
Best, Mahdi