Can I put my Photos library on an external hard drive also used for Time Machine? So, I am new to Macs, and I have a MacBook Air.
I've got lots of phots to import into the Photos program, so I decided to stick them all on an external hard drive.

I have also used that hard drive for Time Machine backups.

Then I saw this warning on the Apple Support page: https://support.apple.com/en-gb/guide/photos/system-photo-library-overview-pht211de786/mac


  WARNING: If a Photos library is located on an external drive, don’t
  use Time Machine to store a backup on that external drive. The
  permissions for your Photos library may conflict with those for the
  Time Machine backup.


My external hard drive simply has a folder for the backups (backups.backupd) and folder called Pictures that contains my photo library.

I don't quite understand the warning. Can the two really not be on the same disk (I don't understand why) or is it saying that I can't use Time Machine to backup the photo library on that disk, which makes some sense...

How are the permissions in the Pictures folder affected by anything that Time Machine is doing? Isn't Time Machine only interested in the backups.backupd folder?

Sorry if this is a dumb question, but I can't seem to find an clear answer.
You can avoid this problem by making two partitions on one drive - one for Photos, the other for Time Machine.
The safest way to do this would be to temporarily move your Photos Library to another drive first, shrink the existing Time Machine prtition, then add a new partition for Photos &amp; move back again.