iCloud Recently Deleted files not working, not fixed after 5 months of Apple investigations, way forward?

See the section if your files don't update to iCloud Drive in this article https://support.apple.com/en-in/HT203052

Make sure you have turned on iCloud Drive https://support.apple.com/en-in/HT204025

And in system preferences > iCloud the box of iCloud Drive is checked , click on option the box of desktops and documents is checked , https://support.apple.com/en-us/HT206985

If the issue still persists first create a new test user account and monitor , otherwise erase the hard drive and reinstall Mac OS https://support.apple.com/en-in/HT204904

If your effected Mac is signed in with same Apple ID and password with iPhone and old Mac with latest version all update and upgrades are performed , if you delete any file from iPhone and older Mac it will be deleted from the Mac ( the files should be synced hundred percent ) and moved to recently deleted folder .

In older iPhone / Mac if you have downgraded the plan the files are kept only for 30 days , as soon as the time period is completely they will also get deleted automatically from recently deleted folder as well from iCloud.com and will not be saved on the iCloud server .

May be you'r data storage is about to reach 30 days ( ie. 2 hours are left ) .

If you create a new test user account and sign in with new Apple ID and password the account data and complete iCloud account is different from previous old Apple ID account , it has nothing to do with iCloud and both have been separated and can't be merged in any way .

And what are your storage plans is it free 5gb or you purchased a new plan , if a new plan is activated the excessive data that was in previous plan will not stay .

Make sure have latest version on all devices and upgrade your compatible Mac with iCloud system requirements https://support.apple.com/en-jo/HT204230

And https://www.apple.com/in/macos/how-to-upgrade/

https://support.apple.com/en-in/ios/update

I have been told it is with the highest ranking technical group and there is nothing to do but wait.

This is not good enough.

I'm afraid it has to be good enough. There is no other path to technical resolution.

Has the senior advisor not responded to you?

As per this article https://support.apple.com/kb/PH27917?locale=en_US&viewlocale=en_US

Recover files deleted from other apps

You can restore files you deleted from other apps, such as iWork apps, in the last 30 days, whether you deleted them on iCloud.com, your iOS device, your Mac, or your Windows computer. However, you can’t restore files you permanently removed as described in Permanently remove deleted files on iCloud.com.

Also https://support.apple.com/kb/PH27916?locale=en_US&viewlocale=en_US