Corinne Durand 
Sorry to hear you've had so much bad luck. However, even in such situations you don't need to give up in the future.

Please consider the following, not very expensive solution: Buy an external HDD. Install this software https://www.goodsync.com/
This license for it will cost you around 30 EUR per year. Connect your new external HDD to your computer. In Windows Explorer you will see the drive letter assigned to it. Remember that. Now start GoodSync and create a new job. When creating a new job, chose "Backup" (One way job). On the left side chose the folder where your working files are, on the right side chose the external HDD. This job will synchronise your local folders with those on the external drive. If you do that on starting your PC and before closing it, no work will be lost in the future.

This is why it would be advisable to keep all your working files on a drive d:\, as then you would only need to synchronise d:\ with external HDD.

Of course there are better ways to backup your work, but this is the most simple one. You can also automate this procedure by adding a timer to it and so on. But at least make sure to copy all your work to an external drive. Your files are your most important asset and you need to protect them. Please consider this advice for the future.

Thank you!

And I spoke too soon, my project does not want to save in Editor, I still get the error message about it not finding the location: It is pointing back the OneDrive to Autosave, somehow (but I am able to save the target file at least, in the new location I have chosen). I hope the TM will save the rest as I work on it, and I can keep on saving the versions of it as I progress, just in case. And will look into the "bigger picture" backup solution. I do have hard drives, so should be able to put that in place when things have calmed down a bit.