Problem syncing Photos

I've been having Photos Library.photoslibrary in an external disk of my iMac.

That disk brooked and it was replaced with a new one but formatted as exFAT.

All data was restored from a backup.

I don't use this computer frequently but some weeks ago I noticed that Photos were not synced from iCloud.

My settings are to have original files in this iMac so the Photos Library is heavy.

Because I found that exFAT format is not allowed to use/sync with iCloud I moved the library to a APFS disk.

When I tried to enable sync in Photos preferences I got this message

My present library file size is 208GB but in iCloud it is 153GB.

How can I fix that?

I know I can delete that library and start syncing from scratch but it is a lot of data to download.

Thank you