Unrecoverable error login window:login

Hi, this morning when turning on my MacBook Pro the login screen would not load. Instead it displayed the following error message:

Unrecoverable error.

SecurityAgent was unable to create requested mechanism login window:login.

It worked fine last night when all it was used for was a Zoom call before being shut down.

When searching for solutions a lot of others refer to a similar error but relating to an error with TeamViewerAuthPlugin:start. This is different to my error and the solutions do not work (thought I would try anyway!). Also I have not, as far as I am aware, uninstalled team viewer.

Does my error message relate to a missing or corrupt file for the login that can be easily reinstated?

I have tried staring in safe boot mode (holding shift) but this does not work. I have also tried the first aid tool on the hard drive as well as reinstalling the OS again (Catalina) but do not have sufficient space on the hard drive. Frustratingly I don’t see the have a recent backup in time machine.

I do not particularly want to reformat the hard drive as I have some data that isn’t backed up...

If anybody has any thoughts for a solution that allows me to login again, I would be very grateful!

Many thanks

Neil