Bottom line is that "Logoff" cannot be erased from the Horizon Client menu bar.
The reason is that VMware Horizon basically assumes that the session control is "disconnect" and "logoff" using the Horizon Client and does not assume that the end user has control over the session on the virtual machine.
I have tried many things.
The Horizon Client menu bar certainly has some functions and other features that are unnecessary for the user. Like buttons that are no longer needed because the administrator has written the config and optimized it.
So some menus can be turned off with GPO.
https://admx.help/?Category=VMware_Horizon_7&Policy=VMware.Policies.vdm_client::HideDesktopMenu_1
However, the minimal functionality of the Horizon Client (Ctal + Alt +Del , Exit Full Screen,
Horizon Client About, Settings, Log off Desktop, Disconnect) are
items cannot be erased.