It is possible to hide and show the palette browser with the little arrow. To hide the filmstrip/image browser you have to hold and move the 3 dots downwards. To show it again you have to hold it again and move upwards.
It would be easier also to click on a little arrow.
" It’s only a little line of source code for a developer, but more comfort for many users" 
Guenter
Dear @platypus
I’ve tried it after your post, but nothing happened. Where did you have your focus by trying this shortcuts?
I’m poor man on Windows
It simply works on my Mac, focus outside of a tool, which is the big canvas, usually…
Ah yes, the magical “little line of code”. Unfortunately, it rarely ever ends up being the simple.
In this case, that separator bar would have to support dual behaviour - one for those who simply want to show/hide and another for those who want to change the size of the thumbnails. And that is not just one one line of code 
So I give you 10 lines…but not more
I have a 27 in screen, with a 4 point font, this will give me a looong line 
Good idea, so on my two 24" screens with expanded desktop and 4 point …I can’t imagine what functions they can design 
Joanna is right with the two functions, but maybe it’s an idea to make the arrow for expand/collapse, mouse wheel for moving the filmstrip if it’s expanded and Alt+mousewheel for sizing the strip.
Was only an idea
On Windows, Ctrl+F9 toggles the image browser presence. The three dots mean that it is possible to resize the browser, which is very useful.
Dear @JeanMontambeault,
thanks a lot…I haven’t seen this shortcut with my blind eyes .
I wish you a peacefully and relaxed Christmas event…stay healthy and optimistic
best regards
Günter
Same for yourself, we all need it. Just think of how much we will be primed for Xmas 2021 !
up until v1 it was already possible to click to hide/unhide, then in v2 this behaviour disappeared. never understood why. but i’d also be happy to have it back…
