ONENOTE : sync error. lost all last months files (lost files not compatible with new version ?)

My local onenote file wouldn't sync for a few months with the oneline version. However i was still able to see a sync between my mac and my iphone.

1 week ago, i noticed that my Notebook would not sync on my iphone either. and yesterday i found out that all my last notes were moved to a new Onenote folder named "MISPLACED" (ii contained very important notes for me). At this point i needed to solve the sync error with the cloud that i was seeing since many months:

• i tried to log in/ log out online or locally but to no avail.
• So I decided that i should updated the version of onenote becasue the version i had was probably to old and causing the issue:

a) before proceeding i made sure to copy the file "misplaced" to a second onenote account and saved a back up as well . However i didn't notice that in the "misplaced" backup file, only 4 sections were actually saved (i probably went to fast ?)!

b) Then, i moved the old version of Onenote to the bin, emptied the bin and installed the new version. after that i could sync my onenote.

c) However, the "misplaced" file disapeared! and it was not on the other account where i copied it either .

I beleive that the new version of Onenote is UNABLE to read the old files . This is why i need to retrieve the older version. i found on this website "Microsoft_OneNote_16.85.24051214_Updater.pkg", but this is still not working. to test it further, i found on my back up files, a recent file and tried to open it and i was still not able to read the file (i am ask to choose an an the open it because it is not compatible with zven this older version)

Should i find an even older version ? i beleive i have version 15.0

Do you know if my files (the one in the displaced folder) could be stored in the older version of ONENOTE app that moved to the bin ? or this does not contain any files of that kind?

Do you think it is still saved somewhere in my hard drive onenote hidden library ? if yes, how to retrieve it ? what should i do ?

Many thanks for your help.

Sandra