modification historical on a pictures

Hi all
Regurlaly , I'm running a backup of my digikam (Raw and Jpeg, DB files , 
appData...) on my NAS

So I do it today, but I see that more than 2K jpg seems have been 
modified since last backup, seems all the same day (30th of October), 
and I'm unable to see what has been changed.
What I'm sure is there is no reason that I may have made any change on 
them (no edit, no tags modification,...) all are old pictures.
DK shows me that files have been modified at that date and when I 
compare the previously saved file and the current one I just see a small 
difference on the size.

I'm running DK8.8 (installed few days before the 30th of October) on 
Win11 (upgraded from Win 10 on 26th of October) and last backup has been 
run before Win11 upgrade (so on 26th of October)

So I have suspended the backup of those files until I can understand the 
reason of the changes.

My questions is then,  how can I compare files ? Is there a way to see 
the historical of modification ?
I selected several files and notice some inconsistencies :
- some have tags on DK but none visible from the The properties/detail 
of the file provided by the windows file manager, neither on the DK 
folder or backup
- some have tags on DK and also visible from the The properties/detail 
of the file provided by the windows file manager on the DK folder but 
none on the backup

So I'm a little lost

Thanks for your help

Regards
Frederic