Resizing doesn't appear to work on macOS Catalina (using iTerm2):

using 0.84 of Terminal.Gui
Using iTerm2 in Linux Ubuntu (WSL) does not fail to resize, but there are many gaps with printing the letters. Perhaps bad mapping related to unicode keys. It seems that some unicode characters aren't properly rendered his lenght in that TERM.

I thought iterm2 was macOS only 馃
I thought iterm2 was macOS only 馃
I think it is but I did change the TERM to iTerm2 and got this ugly view :-)
Just tried this in Terminal.app (the default terminal in macOS and it has different behavior:

Here's terminus as well:

Therefore, it should not be related to GUI problems.