I'm curious, what are the popular products/solutions that LAN centers use for this?

I ended up putting together my own thing. I saw various products that seemed like they might be what I wanted but they always seemed... sketchy.

There are a few, actually :)

CCBoot is a Windows Server-based diskless solution I mentioned, and they also provide CCDisk, which can do "hybrid" mode — where there is a small SSD in every PC with base OS pre-installed and pre-configured, which then mounts an iSCSI game drive

GGRock is a fantastic product, in my opinion. It is pricy, but where as CCBoot relies heavily on knowing it's inner workings, GGRock is pretty much turnkey solution

There is also CCu Cloud Update, which I have heard of, but didn't try myself, since they sell licenses only in Asia, from what I remember

LANGAME Premium is an addon for LAN centre ERP system, which is basically an ITAAS solution based on TrueNAS. Of all paid offerings that one is my favourite so far — but you have to use their ERP and actually run a business for it to be cost-effective

NetX provides an all-in-one (router, traffic filter and iSCSI target) NUC-like server with pre-configured software on a subscription basis. I am most skeptical of that just on the basis that, from my research, two NVMe drives can't really handle the load from a fully occupied 40+ machines LAN centre. Not for a long time, at least

...and homebrew, of course. I myself am running a homebrew ZFS-based system which I'm extremely happy with

In your case, I'd go with building my own thing too. Does not take a lot of time if you know the inner workings and you have no additional OPEX for your room :)

We were running a small internet cafe with gaming computers around 2000 and I found some bootable solution that you installed on every computer. It saved all changes temporarily and flushed everything on reboot, starting from the clean install you prepared the day before. Sadly there was no way of central storage possible with that program. Would have loved to build this setup at that time but money is always short.

Smartlaunch