P: When trying to add files to Collections I get this error: ?:0: attempt to compare two nil values

Try setting Quick Collection's sort order to something other than Custom.

occurs when pushing "B" to move a photo to the quick collection. Running Lightroom classic 10.0

thanks for the workaround!

Leo, see here for a possible workaround:

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-classic-when-trying-to-add-files-to-collections-i-get-this-error-0-attempt-to-compare-two-nil-values/5f9091ea35f40c2520b9ecc4?commentId=5f9473afbd2550489fc119eb 

Why conversations get merged: 

https://feedback.photoshop.com/conversations/lightroom-classic/lightroom-auto-import-to-folders-organized-by-date/5f5f44f14b561a3d422ab0ba?commentId=5f5f48984b561a3d422bdf45 

thank you posted below.

An internal error has occured: ?:0: attempt to repair nil with string

By accident, I found a fix to this problem. I delete all the images in the Quick Collection. Then turned on another collection to be the targeted collection and then right-clicked on the Quick Collection to set it again as the target collection. Now the B puts selected images into the Quick Collection

Please post a screenshot of the error message or quote it word-for-word.

Thank you, just tried that, it updated the catalogue, deleted several years worth, thankfully I know how to fix that, so that s fine. Tried quick collection again, same error message.