Help for Digital Signature Dialog (File => Digital signature) has no information about the button "Start Certificate Manager": https://help.libreoffice.org/7.2/en-GB/text/shared/01/digitalsignatures.html?System=WIN&DbPAR=WRITER&HID=xmlsec/ui/digitalsignaturesdialog/dialog-action_area1#bm_@@nowidget@@
Same issue, same link. *** This bug has been marked as a duplicate of bug 125636 ***