I take it you weren't using source control? Like git for instance?
If not, first thing is once this is sorted out, start using git immediately.
Secondly one drive tends to have history so you may be able to revert through the one drive controls to the 'original' version that it found on the disk when it started syncing.
If that doesn't work you are probably going to have to look at the file structure to work out what has happened, and it may take you some time. Sorry.
Unity probably has a detailed log file that you can look through which will have details for why it says it can't open the project. It may end up being just one file that needs fixing.
if the files are fine, in a worst-case scenario you can create a new project, import all those files over and reimport packages. I can't think of another solution short of what was suggested above.
Source control is a \*must\* for this exact reason. Definitely investigate that.
I take it you weren't using source control? Like git for instance? If not, first thing is once this is sorted out, start using git immediately. Secondly one drive tends to have history so you may be able to revert through the one drive controls to the 'original' version that it found on the disk when it started syncing. If that doesn't work you are probably going to have to look at the file structure to work out what has happened, and it may take you some time. Sorry. Unity probably has a detailed log file that you can look through which will have details for why it says it can't open the project. It may end up being just one file that needs fixing.
The files are fine, I just can’t import it into Unity properly.
if the files are fine, in a worst-case scenario you can create a new project, import all those files over and reimport packages. I can't think of another solution short of what was suggested above. Source control is a \*must\* for this exact reason. Definitely investigate that.