Hi,
Please try different web browers to access below link to see if you can download the app.
https://apps.apple.com/us/app/microsoft-remote-desktop/id1295203466?mt=12
If not, please try if you can install beta version:
https://install.appcenter.ms/orgs/rdmacios-k2vy/apps/microsoft-remote-desktop-for-mac/distribution_groups/all-users-of-microsoft-remote-desktop-for-mac
Thanks,
Eleven
If the Answer is helpful, please click "Accept Answer" and upvote it. Thanks.