The menu bar is only missing in the tightvnc client display :1 whereas it is present in the session connected to a hdmi monitor. On the hdmi monitor session I can open an lxterminal (about says 0.3.2) from the menu bar (LXDE). Whereas right clicking on a folder and "Open in Terminal" gives me an Xfce terminal (about says 0.8.7.4).
In raspi-config the default display resolution was not changed. The black border around the screen on the hdmi monitor was removed. (I have the same settings on an rp3b+ with an older install and have no problems with the menu bar, also using tightvnc).
I was not able getting the menu to show up.
The fresh install was done with "Raspberry Pi Imager" and chosen "Raspberry Pi OS (32 bit) published 2021-03-04". (I tried it twice with the same result).
Operating System: Raspbian GNU/Linux 10 (buster) Kernel: Linux 5.10.17-v7l+
Changing the geometry (resolution) of the vncserver process doesn't help.