Lightroom freezes opening any version or backup of one catalogue.

Try resetting your LrC Preferences file. It is not updated when you do a reinstall and may be corrupted. Move the .plist file to your desktop as outlined at the below article. That way you can easily restore it if of no help.

https://www.lightroomqueen.com/how-do-i-reset-lightrooms-preferences/

I have a really weird situation where I cannot get a catalogue to open. When I try to open it I just get the first Lightroom loading graphic before it stops responding and the following files seem to cycle appearing and disappearing in the same container as the catalogue -
.lrcat-smh
.lrcat-wal
.lrcat.lock

I think this is expected to happen. So that's not the problem.

If it is always the same catalog (and recent backups of this catalog) causing the problem, then try this:

Open a different catalog, then File->New Catalog, then File->Import From Another Catalog and select the problem catalog file.

Hi, 

Thanks for reaching out! We are sorry about the trouble with Lightroom Classic. We are here to help!  

Could you please share the exact version of Lightroom Classic along with your operating system on your macOS computer? Please specify where the catalog is stored, are they stored on an internal drive or an external drive?  

If the catalog is stored on an external drive, please move it to the internal drive or desktop and try launching it from there. Please check here for more help related to Lightroom Classic Catalogs:  

https://helpx.adobe.com/lightroom-classic/kb/catalog-faq-lightroom.html 

Also, please ensure Lightroom Classic has permissions needed on the Mac by following the steps suggested below:  

1.  Go to the System Preferences for your Mac, then Security and Privacy, then select the Privacy tab.  
2. Then select Accessibility from the list to the left & check if Lightroom Classic is added to the list with a checkmark in front of it.  
3. If Lightroom Classic is not a part of the list, please add it by unlocking the window first using the lock at the bottom left, then clicking the + icon & navigating to the Applications folder.  
4. Also, grant permissions to Lightroom Classic under Full disk access found in the same list as Accessibility. It should look like as shown below. 
   
5. Once done, restart the Mac & check if it helps. 

Please let us know if this helps!  

Regards, 

Sameer K.