LrC Crashes on Startup, Mac OS 12.6

Make sure you have provided "Full disk access" to LrC. See instructions at the link below.

https://community.adobe.com/t5/lightroom-classic-discussions/quick-tips-how-to-give-full-disk-access-to-lightroom-classic-on-macos/td-p/12913413

On another note, I have an iMac mid-2015 which is using macOS Big Sur due to the fact that my Mac is not supported for Monterey, so you need to prepare for "end of life" for your Mac. It's unlikely it will be able to upgrade to the upcoming macOS due to be released in a few weeks.

I have struggled for the past year in getting "security" updates for Big Sur installed. The latest one has failed.

Maybe a visit to an Apple Store

On the problemaic Mac: 

Try logging into another account (you may need to make one), still crashing? 
Try starting up in Safe mode (hold down Shift Key when booting), still crashing? 
You might want to try running a free utility like Onyx: still crashing? 
https://www.titanium-software.fr/en/onyx.html
Also view:
https://www.macworld.com/article/352902/onyx-review-macos.html
https://www.macworld.com/article/224955/how-to-reset-a-macs-nvram-pram-and-smc.html
From Adobe:
https://helpx.adobe.com/photoshop/kb/basic-troubleshooting.html

Solution
This issue occurs when Lightroom Classic is configured to Use Graphics Card in the preferences with DirectX enabled.

To resolve this issue, follow the steps listed below.

Update your graphics card driver.

On your Windows machine, download the most recent driver directly from your graphics card manufacturer's website:

NVIDIA drivers
AMD/ATI drivers
Intel drivers

Perform a clean installation of your graphics driver

When upgrading the graphics card driver, it is recommended that you remove all previous versions of the graphics card driver from your computer before installing the new one. This is called a clean installation.

Once you’ve determined the make and model of your graphics card in your computer, follow your card’s manufacturer documentation and resources below:

NVIDIA drivers: How to perform a clean installation of my Nvidia drivers?
AMD drivers: AMD Clean Uninstall Utility
Intel: Intel Driver & Support Assistant (Intel DSA)
After installing the updates, relaunch Lightroom Classic.

Note:
Windows update won't always give you the latest and greatest drivers. You must go directly to your card manufacturer’s website to check for driver updates.
Be sure to choose the correct driver. Notebook drivers sometimes have a different name than similar desktop drivers.
Some video adapter manufacturers have other software that requires updating in addition to the video driver. Read the update instructions carefully, or contact the video adapter manufacturer directly if you don't understand the instructions.
Turn off the Use Graphics Processor option.

In Lightroom Classic, choose Edit > Preferences.
In the Preferences dialog, click the Performance tab.
Deselect Use Graphics Processor.
Relaunch Lightroom Classic.
The crash issue should now be resolved.

This may help you,

Rachel Gomez

Admin / Moderators, the author has duplicated this exact post as a Bug, please fix.

Author, not a bug, other members with exact same rig not having this problem.

1. In the Adobe Creative Cloud Desktop App, sign out, the sign in, any errors? Any notes?

2. Are you sure the verifying message is via LrC? and not your MACOS? MACOS message would look something like:

That occurs whenever you launch a new or updated/upgraded application. It is a MACOS security measure.

In LrC, verification would not occur if you are signed in (Adobe Creative Cloud Desktop App) when launching LrC.

3. Have you simply tried to reboot your computer? Some members with MACOS after seeing a MACOS verifying message found LrC worked after a reboot.

4. You did upgrade the LrC via the Adobe Creative Cloud Desktop App? 

App version(s):

11.5

Mac OS version: 12.6, iMac (Retina 5K, 27-inch, Late 2015), 3.2 GHz Quad-Core Intel Core i5, 32 GB 1867 MHz DDR3

After the update to LrC 11.5, I cannot get it to launch at all. I'm on Mac OS 12.6 (Monterey).

I tried resetting, and then entirely removing, Preferences of all kinds in every Library folder (user and system level). I've now completely uninstalled 11.5, rebooted, and reinstalled, and rebooted again. And have now tried going back multiple versions, all the way back to 10.4, repeating the same process every time:

1. attempted launching while holding Opt-Shift and/or Opt-Shift-Del to reset preferences, or manually removed preferences in Library

2. uninstalled entirely, rebooted, and installed a different version fresh, rebooted, and attempted to launch

I've used LR since the original beta, and have never had this level of issue before where it would not launch at all, regardless of version of the program or operating system.

What happens is, after a fresh install of any version from 10.4 on up to 11.5, I click the app icon, it says "Verifying" (as usual on first launch after installation) and then the splash screen shows for a few seconds. Then...it disappears. The icon shows that it is not active at all, as if it were never clicked. No error message, no crash report, either from Adobe or Apple. Nothing. It's as though I've not tried to launch it at all.

And, yes, I've moved all prior catalogs from their default locations in effort to have LrC launch with a fresh untouched catalog, to rule out the possibility that one of my catalogs was corrupt. Holding Option/Alt to force a Choose Catalog window to appear, beacuse it never gets that far.

Help? I typically use LrC every day in my business for multiple client catalogs, and have been attempting to fix this through uninstalling/reinstalling 10 different incremental and one major version (10.4 through 11.5) by various approaches for two weeks now. It's killing my productivity and ability to work with my client files efficiently.