Please have a look at the attached screenshot. These undo and redo items are redundant in the menu since these items are present as buttons directly above the menu button.
Created attachment 150352 [details] Screenshot
The actual layout of Notebookbar variants is up to the designer. Redundancy is per se not bad and I cannot argue whether or not having double it. It just depends on the design.
andreas kainz committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/core/+/22d79472b6f395a2b4de74dc360bf8e61b1028e3%5E%21 tdf#124392 remove undo/redo commands from groupedbar drop down It will be available in 6.3.0. The patch should be included in the daily builds available at https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: https://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.
Andreas, please resolve this ticket as fixed if done.