error lightroom

@Ian Lyons  I think you meant to say downgrade to V 10.0.

Edited to fix LrC version number

The issue you describe is most likley caused by a GPU conflict introduced by Big Sur. You have two options:

1. Disable GPU support in Lightroom Classic Perferences (Performance tab)

2. Downgrade to Lightroom Classic 10 using the Creative Cloud App

Unfortunately, disabling the GPU can result in reduced performance when using some tools within the Develop module (e.g. local adjustments, texture, clarity, dehaze and noise). Therefore, if performance is important, then you may wish to revert to LrC 10. The process is quite simple when using the Adobe Creative Cloud App.

• Launch the CC App
• Choose All Apps
• Click on the 3-dots button to right of Lightroom Classic
• Choose 'Other Versions (see below screenshot).

Note that you do not need to unintstall 10.1 as this is handled by the version downgrade process.

This is a known issue on some Mac by Adobe. You should try rolling back to Lightroom Classic V 10.0

In the Creative Cloud app list of applications, click on the dots to the right of the Lightroom Classic listing and select "Other Versions". Select V10.0

Advise if that works for  you