From release notes 7.6: Added support for drawing styles for shapes and comments. This includes a dedicated style for comments that makes it possible to customize the default look and text formatting of new comments. The old workaround involving editing the default cell style was removed. commits (Maxim Monastirsky) https://gerrit.libreoffice.org/q/owner:momonasmon%2540gmail.com+drawstyles
Olivier Hallot committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/ac281f6182dbb4ba1190c7bf89bfd693c58d6c5c tdf#156441 Add help page for Calc drawing styles