Unfortunately, as convenient as it is, mega, drive, etc. if you upload the thumbnails directly, their system automatically deletes them....
The best is to compress them in a *.rar, *.zip, etc. file.
I leave again mine in that format. You will have to download it, unzip it and view them locally on your computer.
https://mega.nz/file/JbV3EBKD#G27n6h...FOq589XCznDLfI