Since version 7.0, toolbars are locked by default (see bug 92484). So in the default UI, toolbars don't show any handles, and have to be unlocked before they can be moved or undocked. The current help page for toolbars https://help.libreoffice.org/7.2/en-US/text/shared/guide/floating_toolbar.html doesn't mention the locked/unlocked status of toolbars at all, and the "To Make a Toolbar a Floating Toolbar" section talks as if the toolbars are unlocked by default, and causes users' confusion like bug 139101. That help page probably needs improvements in many places, and mentioning the locked/unlocked status, as well as telling users to unlock the toolbar before further actions would be a good step.
*** Bug 139101 has been marked as a duplicate of this bug. ***
I gave it a try at: https://gerrit.libreoffice.org/c/help/+/108297
Ming Hua committed a patch related to this issue. It has been pushed to "master": https://git.libreoffice.org/help/commit/eec60108b90928b81d094f7f37250164467d8cd6 tdf#139122 Add information about locking/unlocking toolbars