This also seems common in KDE Plasma, too. What they both share, but Gnome lacks, is Windows Compositing (Since Gnome generally does little in the way of Window Management).
On XFCE, you might try:
Open Settings, then move to Window Manager Tweaks > Compositor
Uncheck "Enable display Compositing"
You might also uncheck Shadows....
Refresh your desktop and Test Zoom.
You may also check your Refresh rate for your monitor.
Can you explain the explain the question in detail please?
Try it in window mode instead of fullscreen, i have seen people posting that that fixed the flickering for them.
Yes there is no flickering when in window mode but that does not slow transition, breakage of some controls. Most of the time I want to be in full screen because the notes and documents shared will correctly fit to be visible and to write.
The only thing you can try for now is to follow @Aravisian's post Zoom meetings keeps on flickering while on fullscreen - #7 by Aravisian
After I have unchecked "Enable display Compositing" it looks like
And could not find any Shadows option
What if you hit the button "all settings"
Whaaaat...
I am on Zorin OS 16 Lite:
I wonder why you have fewer setting options.
What is terminal output of
xfwm4 --version
Oh... You needed to scroll down... 
What if you increase the size of the window to approx full screen size. Does that then give you the Zoom controls etc?
So which shadows I need to disable? All?
I meant both, just for testing it.
Did not work unfortunately.
Ok. You may want to reenable those settings, then.
Have you checked your Refresh rate?
xrandr
Screen 0: minimum 8 x 8, current 1024 x 768, maximum 32767 x 32767
LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 290mm x 210mm
1024x768 60.00*+ 50.00
1024x576 59.90 59.82
960x540 59.63 59.82
800x600 60.32 56.25
864x486 59.92 59.57
640x480 59.94
720x405 59.51 58.99
640x360 59.84 59.32
512x384 60.00
DVI1 disconnected (normal left inverted right x axis y axis)
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)
I would think this should be 59.89 or 75.03
Can you please test:
xrandr --output LVDS1 --rate 60
If no good, try:
xrandr --output LVDS1 --rate 75
Thanks but the flickering is still there after trying the terminal commands
but I found one thing to do to avoid flickering that it to right click on system tile bar and enable "Always on top" and then to resize zoom in such a way that it hides the panel.
By this, zoom will also be at full screen and no flickering will be noticed because it only hides the panel to make it look like it is in fullscreen
Yes resizing it to approx. full screen by enabling "always on top" avoids flickering and breakage is not that much
