A partition that is visible but not accessible, how to do it?

I have an old ASUS laptop initially running Windows 7 but upgraded to Win11.
It was slow so much that it was unbearable, I doubled the RAM to 8 GB instead of 4 GB and changed the HDD to an SSD.
 
It's day and night, the cell phone has found a real catch.
 
Basically it has 2 HDDs of 500 GB each and each HDD has 2 partitions
 
The 1st DD C: and D: is replaced by the SSD on which I installed Win 11
 
The 2nd HDD: when I open "this PC" it appears in C: the SSD and only one of the 2 partitions (SDATA2) of the HDD the SDATA1 is invisible but in the hard drive manager it appears.
 
I don't understand why this partition is invisible?
 
Do you have a clue to make it reappear without data loss?