An M.2 NvME drive can be plugged into a PCI Express slot using an adapter card, basically.
Another aspect which I forgot to mention previously, is whether you have a high-speed Internet connection or not.
Since I am still on 20 Mbps, a 40 GB download can take in the whereabouts of 8 hours undisturbed (meaning the connection isn’t used for anything else).
For this reason, i usually start large game downloads in advance and let them run throttled for as long as it takes. If it turns out I’m not going to play them in a reasonable time frame, the games get backed up to an external drive.
So if you’re on a slower Internet connection for which downloading in advance is preferred to having to wait for however long before playing a game, extra space gives more breathing room.
All things considered, running a roomier, cheaper mechanical drive in tandem with the SSD can also offer a stopgap solution to the problem of storing large games that you’re not going to play immediately.