In the help page for customizing keyboard shortcuts (searched by "customizing -- keyboard", 6.3 online URL https://help.libreoffice.org/6.3/en-US/text/shared/01/06140200.html ), there are two paragraphs in the "Modify" section. The second paragraph obviously discribe the "Delete" button instead of the "Modify" one. It seems a section title "Delete" is missing. I checked both my local 6.2.8 version and the online 6.3 version, and the problem exists in both. Don't know an easy way to check master/6.4 so didn't check.
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/ec3711dbe4d9cee407cbf7e6707cfaf15860c490 tdf#128427 Add 'delete' heading in custom Help pg