It is very hard to resize a window in Ubuntu 20.04. The resizing UI widget has to be precisely placed (< 5 pixels).
The answer to How do I increase the resize margin on windows? does not work for 20.04.
How do I increase the resize margin in 20.04?
It is very hard to resize a window in Ubuntu 20.04. The resizing UI widget has to be precisely placed (< 5 pixels).
The answer to How do I increase the resize margin on windows? does not work for 20.04.
How do I increase the resize margin in 20.04?
Various workarounds posted to the other question you mentioned are still usable on Ubuntu 20.04 though.
For example, the workaround mentioned in the top scoring and the accepted answer still works in a sense:
The only difference is that on Ubuntu 20.04 the default window action key is Super (usually the key with the Windows logo) instead of Alt. So you can resize windows by pressing and holding down Super and then middle mouse click and drag.
You can also change your window action key to Alt using (GNOME) Tweaks. Launch Tweaks and change the key for the 'Window Action Key' option in the 'Windows' section.
Similarly, the Alt+F8 trick mentioned in this answer also works fine on Ubuntu 20.04 and so does the right-clicking on the title bar and selecting the 'Resize' from the context-menu trick as mentioned in another answer.