Problem:
The Keyword List has a number to the right of each keyword for the number of photos that have this keyword. To the right of the number there is an arrow that one can click, which results in displaying the catalog 'All Photographs' filtered for those photos that have this keyword. However, if photos are part of closed stacks, this method will not find the photos.
Therefore, the smoothest solution to this problem is to make the catalog 'All Photographs' always show all photos as unstacked.
The problem is slightly related to the discussion in https://community.adobe.com/t5/lightroom-classic-discussions/lightroom-classic-not-finding-photos-in....
There are workarounds, such as https://www.danhartfordphoto.com/blog/2022/4/lr014-lrc-tip01-all-photos-really, but none are as obvious and smooth as if it was possible to simply click on the arrow to the right of the keyword in the Keyword List, directly listing those photos.