All images missing after mac update

Check that Lightroom Classic has the necessary permissions.

Mac OS upgrades seem to love to mess with user permissions on disks.

Check the Folders panel in Library. If the folders are marked with "?" LR cannot see them any more. Using Finder, check the drive permissions and folder permissions.

LR understands the difference between missing files and files in missing folders. You need to fix the folders first. (If that is the problem.)

Unfortunately for you, I'm a Windows user and know absolutely nothing about the Mac. I know, the Mac is simple, but that doesn't help me. The easiest way to resolve the issue is to ensure that those two external drives are being recognized by Lightroom with the exact same names as they have always been recognized by. If those names have been changed somehow then rename them. That would immediately solve the problem as far as I know. As an alternative, you can click on each folder or on a master folder that has subfolders in the library module and choose the option to update the folder location and point Lightroom to where the images are now located. It seems to me from what you have indicated that your system has lost the identity of those two external hard drives, and it's up to you to get that straightened out.

Lightroom is the name of the program that stores your images in the cloud unless you are using a very old version. Lightroom Classic is the version that utilizes a local catalog and stores images in folders on your local hard drive. Please clarify the exact version of Lightroom you are using. Are your images being stored on an external hard drive?

Forgot to mention that this is happening in Lightroom!