Buster: zz-mass-hosting doesn't appear to work.
On boot, it's sending traffic to /var/www/html, and then after reconfiguring it seems to be only sending traffic to /srv/$localhost/public/htdocs.
It may be due to changes in the newer Apache breaking dynamic vhost configurations in general, or something else like the custom module not working right any more.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information