Photoshop will not start

What plugins do you use?  A lot of plugins exist as .8BF files in wherever the plugin folder is on a Mac.

With Windows it's:

Make a new folder and drag the contents to it from the plug in folder, and when backed up, delete the originals.  If Photoshop now starts OK, you can drag the plugins back one at a time till Photoshop fails.  This may or not help, as only about half of my plugins live in that folder.

When you start Photoshop with the Shift key, you are eliminating all third-party plug-ins. One or more of those plugins may be causing problems.

See if this guide helps: https://helpx.adobe.com/photoshop/kb/plug-ins-photoshop-troubleshooting.html