I actually managed to get in touch with MS support up to 3rd level support and the problem & resolution description was at follows:
1.PROBLEM:
In short - Mac OneDrive app is full scanning even when not needed and if you do a lot of file sync - it's eating up CPU like crazy.
"Clearly, we've had some limitations and I want you to know that getting to the bottom of this is just as important to us as it is to you.
Unfortunately, this is expected behavior. I was able to repro it myself. Whenever Excel saves a file, it bumps the last modified time on the parent folder, which triggers a full scan on Mac. This is an area we're actively working on improving (by eliminating these full scans), but we don't have an immediate solution."
- "RESOLUTION":
This is the answer I got from engineering.
“we'll be working on it more next semester, we expect it to do be done sometime in that time period”
I added your name along mine on the item that engineering has in the backlog. As soon as we do have an update, I let you know .
In case we have a beta product I will let also know. you will be able to test and let us know the results .