My suggestion is to use system management tools like Foreman. It has a “content views” mechanism that can do more or less what you want. There’s a bunch of other tools like that along the lines of Uyuni. Of course, those tools have a lot of features, so it might be overkill for your case, but a lot of those features will probably end up useful anyway if you have that many hosts.

With the way Debian/Ubuntu APT repos are set up, if you take a copy of /dists/$DISTRO_VERSION as downloaded from a mirror at any given moment and serve it to a particular server, that’s going to end up with apt update && apt upgrade installing those identical versions, provided that the actual package files in /pool are still available. You can set up caching proxies for that.

I remember my DIY hodgepodge a decade ago ultimately just being a daily cronjob that pulls in the current distro (let’s say bookworm) and their associated -updates and -security repos from an upstream rsync-capable mirror, then after checking a killswitch and making sure things aren’t currently on fire, it does rsync -rva tier2 tier3; rsync -rva tier1 tier2; rsync -rva upstream/bookworm tier1. Machines are configured to pull and update from tier1 (first 20%)/tier2 (second 20%)/tier3 (rest) appropriately on a regular basis. The files in /pool were served by apt-cacher-ng, but I don’t know if that’s still the cool option nowadays (you will need some kind of local caching for those as old files may disappear without notice).