Help for Insert Rows says its in the Insert menu -- its actually in the Sheet menu, and there's no longer a keyboard shortcut (used to be Alt-I-R).
You can get some information about menu changes in: https://wiki.documentfoundation.org/ReleaseNotes/5.1#Reorganization_of_the_menus Added UX.
No idea why should the UX-Advise list be spammed with bugs like this. It is enough to block the help meta bug.
Patch submitted to Gerrit: https://gerrit.libreoffice.org/#/c/22405/
Stanislav Horacek committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/help/commit/?id=fd91f34b3106eea47e8378a672d5a42fe2920b00 tdf#97807 Calc menu changes for inserting rows and columns