PowerPoint found a problem with content in

I saved a PPTX file yesterday (in a folder on my PC synchronized with OneDrive). Today, I cannot open it, only getting a message: PowerPoint found a problem with content in.... PowerPoint can attempt to repair the presentation. If you trust the source of this presentation, click Repair.

When I click on Repair, I get a message Sorry, PowerPoint can't read ...

I tried several options I found on Internet:

+ In Properties, there is no option for trusted sites, as also recommended

+ I copied it into a folder not connected with OneDrive - Does not help

+ Marked file location as Trusted Sites - Does not help

+ Purchased Repairit - File Repair - Does not help (I only got some pictures from the original file)

As the presentation is for my wife's birthday which is in 2 days and it took me 3 week to build it, I am pretty worried now...

Any idea how to fix it, please?

Thank you in advance!