You're welcome! scratch and distroless are indeed basically the same thing, scratch being the 'official' docker minimal image while distroless is from google - as I'm more a Kubernetes user (at home and at work) than a Docker user, I tend to think about distroless first :) - my apologies if my comment was a bit confusing on this matter.
By the way, have fun experimenting with docker (or podman), it's interesting, widely used both in selfhosting and professional environments, and it's a great learning experience - and a good way to pass time during these long winter evenings :)
It's possible to write very complex rules/ACLs with HAproxy... stick-tables, ACLs with regexes on whatever HTTP header, source or destination ACLs, map files, geoblocking, lua scripting, load-balancing from round-robin to host header load balancing, dynamic backend servers provisionning through DNS... Not that you can't do it with Nginx (it started as a reverse-proxy before becoming a jack of all trades), nor that nginx isn't a great tool (it is!), but HAProxy can do very complex things too. It also follows the good ol' UNIX philosophy of "one program to do one thing and do it well" and thus doesn't try to be a webserver, hence why you need a webserver behind it to serve anything from static files to PHP/Python/whatever.