I would always recommend good old Debian for a mostly „it just works“ experience. You‘ll find debian packages for most if not all the things you mentioned. Alternatively you could go the steeper route and use an immutable OS like Fedora CoreOS or Fedora Silverblue for a more desktopy experience.

Hardware wise I‘ve been told the Intel NUC kits work wonders, or similarly specced boxes from Asia. You might get like 32GB RAM, a fairly recent CPU for <400€. Personally I‘m using a 12 year old Mac Mini until it dies, running debian.

Steam does this as far as I know.

Most likely CD is intended to mean continuous delivery, which commonly means automation in processes that deliver your software to it’s target audience.

Ungeöffnet in den Sondermüll werfen, musste ich auch schonmal…