Thanks for the explanation. I'll just stick with the way I am doing it.homebrew (see brew.sh) is often mentioned as "the app store for the command line". It has no GUI and is entirely based on terminal commands. Its origin is as a central easy-to-use means to keep all command line tools up to date, but later on they also included GUI-based tools as so-called "casks" (for example Onyx can also be installed as a cask via homebrew). Keeping all tools up to date is indeed easy: one single command "brew upgrade" enables a batch run which updates all of the tools you installed via homebrew to their most current versions.
BTW, the bug in Apple Mail (not being able to move emails into iCloud IMAP Folders) re-appeared. Easy to temporarily fix again via Onyx, but it looks like this is still a persisting bug in Catalina 10.15.7.
Also, sure is perplexing that an Apple program, Mail, and a critical one at that, would still have issues. One would think Apple could fix that. But I decided a long, long time ago not to use Apple's Mail program, as problems seem to exist with it no matter which mac OS one is using. Thunderbird, while not as "sexy" looking, works flawlessly.