As for whether it would be buggy, I'd doubt it? Unless Black's principle of operation is different from most formatters, it should just write the formatted contents to the file, right? The autocommand you'd use would just run Black on your current file on each save. So where % is Vim's symbol for the name of the currently open file, :silent! suppresses stdout/stderr from the formatter, and :! runs a command:
autocmd BufWritePost *.py silent! !<format_cmd> %
(Don't quote me on that, but it should be essentially correct. I'm not at a computer right now.)
Actually, it looks like you can install an (n)vim plugin from the official Black repo here:
https://github.com/psf/black/blob/main/plugin/black.vim
And then the autocmd would be
autocmd BufWritePost *.py silent! Black
This stuff is documented here: https://black.readthedocs.io/en/stable/integrations/editors....
Anyway, I think it's actually a really cool effect of doing this that you realize a lot of the scaffolding underneath most editors _isn't_ that complicated! It's totally understandable :)