Lost photos after updating my Mac mini to macOS Sequoia 15.5

KyleKursk wrote: … I was hoping someone would have come back with a response that Apple knew it was a problem and to just wait till they put out another version that fixed their problem. .

Yeah-- everyone kinda hopes it's something Apple did wrong! But we've been using Sequoia for nearly a year, now, and Photos works great with it.

On a Mac you can have multiple Photos Libraries. When Photos first opens, if it doesn't see a Library it knows, it makes a new empty one and pleasantly welcomes you. So it may be that Photos doesn't know which Library you want to use. The easiest way to tell it is to go to the Library you want and double click it-- that should open Photos with that Library, and Photos will remember next time. This may be all you need to do!

Of course, it could be something different-- it's hard for us to know.

As to the disk format, it's important to know, although your Geek Squad probably set that up correctly. To find out, though, you can click on the name of the Drive (you might see it in the Finder's sidebar or on the Desktop) and use Command-i (⌘ i ) to get its information. Mine, here, is APFS.

It's very important that it not be ExFAT! Also, as Matti Haveri alluded, the Library can not be on the same drive as Time Machine.

Let us know how it goes. And if you need more help, we're here. If you get back in touch about a problem, let us know the following stuff if you can:

• What models are your devices? (You listed iPad, but asked us about a Mac-- a bit confusing.)
• What OS and/or iOS and/or iPadOS are you using? 
• Are you using iCloud Photos to synchronize your devices?
• Do you have “Optimize Storage” checked in Photos’ Settings?
• What percentage of your storage is free?
• Have you tried re-starting your Mac (or iPad or iPhone) since the problem began?

In fact on every update documentation page, it recommends you backup your data. In addition they have an extensive guide on backing up your data:

How to back up your Mac - Official Apple Support

They even provide two facilities to backup called iCloud and Time Machine, and the Finder itself offers manual copying of files. Never assume computer data permanence. Now you have a couple options:

Locate files with Devon Technologies EasyFind or Mark Tempel's FindAnyFile.

Read this tip on data recovery.

Lastly, many Apple Authorized Service Centers offer data recovery services.

KyleKursk wrote:

We have our photos on an external hard drive if that means anything.

Is the external drive formatted as APFS or MacOS Extended as it should??

Other formats like exFAT, FAT, NTFS, network shares, Time Machine volumes are not supported and might corrupt the library.

Move your Photos library to save space on your Mac - Apple Support

And do you regularly backup that external drive because all drives eventually fail?? An extra backup before any update is also recommended.

The glitch also is in not knowing how pictures are stored on a Mac.

Users -> yourname -> Pictures stores photos Apple Photos App is asked to manage through its preferences. This Folder is actually an Archive folder, which can be opened through control mouse click to view the contents. Don't modify the contents inside otherwise Photos App may get confused.

iCloud syncing of photos to appear simultaneously on iDevices as your Mac, may make it appear as those this folder has disappeared by is actually residing inside your On iCloud folder. Double check that http://www.icloud.com/ doesn't have your photos as a result of that syncing.

If you ask Photos not to manage your photos, you can strictly guide the Finder to put the photos in their own folders away from synchronization folders such as iCloud and OneDrive, so they never are delayed due to how your Cloud sync manages your photos from appearing. This may be what happened after an update as the system is trying to ensure to backs up everything.

If you use FileVault or other encryption method, the disappearance of files from the Finder may only be temporary as FileVault rebuilds its database and encryption after an upgrade. Background optimization apps can also delay the reappearance of files after an upgrade. Don't use optimization tools like MacKeeper, Advanced Mac Cleaner, etc.

Well not exactly. It really is your not understanding what the Geek Squad did to setup the drives.

This is why recommend using those search file utilities that are independent of Spotlight to locate the files.

If you have some idea of the name of the photo or the date they were created, you can search your hard disk for those files, or any of those hard drives. Once you know where it stores the files you are better.

Time Machine many people don't understand how it operates. It is not a true clone.

It operates on recursive backup principle deleting the older less used files once the backup gets too full and are no longer on the original. When you turn off Time Machine, you have the opportunity to copy the archive files to a secondary space not touched by Time Machine so that if it does delete on Time Machine backup, you don't lose them. The advantage of Time Machine backup, is Apple's migration tool brings over any data that is found to a new Mac when initially setup. And while the interface to search the backups is nice, it is also dependent on the accuracy of the Spotlight index taken of that drive. If you don't index Spotlight, you might find files appear missing from either Time Machine or the Finder. That's where Mark Tempel's or Devon Technology's software comes handy.