Screen flickers

[obcat]

If there is only one window, screen flickers while scrolling.

Environment

• Vim 8.2.1950
• macOS Catalina (version 10.15.7)
• iTerm2 and terminal.app

Others

This does not occur in gVim (MacVim).

[obcat]

This happens whenever there are any popup windows.
Probably a problem with Vim itself.

cf. vim/vim#4458