After rebooting my computer, the team project I am working on, has 'reverted' to a 3 day old version.
By the looks of it, I have lost about twenty hours of work. I have browsed 'previous versions' and 'autosaves' in the cloud but to no avail.
So I am hoping: Is there any (hidden) local file that I can use to recover?
Are you logging in from the same machine, using the same machine login and Creative Cloud login? Your latest auto-save should be visible in the Media Browser from any machine if you log in with the same Creative Cloud ID, but the history of auto-saves you've made on a particular machine is only available on that machine. It is stored in a per-user directory, in a versioned database. On the Mac, your auto-save databases are stored in /Users/your-user-name/Library/Application Support/Adobe/Common/Team Projects Local Hub/. On Windows, they're in C:\Users\your-user-name-\AppData\Roaming\Adobe\Common\Team Projects Local Hub. The database format is not documented, but that's where the data is.
Did anything happen to you machine that might have compromised one of those directories (i.e. a hard drive failure)? Were you able to exit Premiere/After Effects cleanly before you rebooted? If so, any unsaved work should have been saved to the local database at that time.
If you're logged in on the same system, with the same computer account and Creative Cloud account, you should be able to navigate to the Team Project in the Media Browser and switch to the auto-saves tab. There's a slider on the right side of the window that you can use to scroll back to previous auto-saves. If you scroll back to an earlier one, you can make that one the latest one by right-clicking the Team Project name and choosing "Make version (...) the latest". Doing so will not erase any auto-saves, just update your Team Project to match that earlier auto-save state. You can go back to any auto-save in-between if needed.
I have been working on a team project in Premiere Pro 2020 for a while. And today one of the editors of the project mess up with one of the timelines. I had no idea of that and when I pressed "Get Lastest Changes" I imported all of his mistakes. How can I restore the previous timeline that I was working before I imported his changes?
You can import a previous version of the 'messed up' sequence into the Team Project.