I'm using a custom made add-on; a fork of this to do the reverse; to do quoted -deepcat searches outside of the cat we are looking at and it works well after a certain fix around this kind of bug. This update can be seen here: https://commons.wikimedia.org/w/index.php?title=User:Samwilson/Searchnotincat.js&diff=next&oldid=933232426 So here might be found a hint or an example of what a possible fix could look like. This fork works well.

Hi, the More button on category pages appears for logged-in users if in their user preferences in Gadgets are set to use some of the Aids for Categorisation: option 4 and 6 should be checked : 4=add search links ... 6: Deepcat Search. After that the More button should be visible on top menu next to history tab. Thanks

Hi OK, tx. it's here: https://phabricator.wikimedia.org/T415398

Today I found a bug in cases where the category name has an "&".
Example: deepcat:"Pellerin & Cie" Try a deepcat search in deepcat:"Pellerin & Cie" > results in this search: deepcategory:"Pellerin_ No matches because of the wrong folder name. The folder name is truncated at the "&".
I know there must be a patch for this since my branched button that automates " " -deepcat:" " (such as "Pellerin & Cie" -deepcat:"Pellerin_&_Cie") has this a patch been applied already for a longer time and works well at this point time. The fork is hosted and patched by User Samwilson.
I hope the regular deepcat function can be patched for this issue without damage to the opposite -deepcat searches.

On commons we want to have the option to enable all thumbnails completely, not mocked up pseudos like cropped squares. To give image researchers fast ways to overlook their search results seeing the exact image contents as miniatures, including all edges. For example to see if it is a landscape or portrait format. Thumbs of image files on Commons do need this special attention compared to thumbs on other projects.