On the definition of DRM

Warning: This is a rather thorny question, in the same style of debating if a particular product or software is under a FLOSS license or not. It's also deeply linked to laws, and I am not a lawyer, do not take this as legal advice.

That aside here's how I define DRM as: A juridical backdoor which serves to restrict more or less fundamental rights like private copies, private modifications and effectively interoperability (which is one of the copyright exceptions in the European Union).
I see technical means as irrelevant or even a gigantic trap, PDF for example uses a bit flag to restrict printing, making it effectively non-existant if you're not following the PDF specification to the letter.

• What's the difference between a mere mod (legal privately, redistributions of them are typically tolerated) and a crack (illegal, always)? DRM.
• Is a software or network dependency a DRM? Not on itself, it becomes DRM if becomes illegal to circumvent it (Some of those dependencies are particularly annoying and ought to be avoided though).

Steam

This is a rather controversial part, but I want to address it. My position on it is:

• A lot of games rely on Steam (sometimes only for achievements): It becomes DRM if fixing the hard-dependency via mods or a shim is illegal or not;
• There's games on Steam ship with Denuvo and other DRM solutions, I don't remember if those are explicitly noted as such;
• The main steam client (steamcmd even if official is excluded here) itself is a deeply annoying games installer with forced auto-updates, making usage of it offline a challenge. I'd call this a botnet, not DRM.

Or said otherwise Steam is an unfortunate vector for DRM, quite like a CD player is with games trying to require physical copies of CDs to be present for playing. And just like the CD-era, it is hard to know if a particular game has DRM or not on Steam, much better to bet and support stores with a stance against DRM.

And personally I much favor games where I can get the art under whatever licensing/price and get the software part with source-code under a libre license (or be able to use third-party software), for example Quake 1&2, Doom 1→3, and Visual Novels using a generic multimedia-player style of architecture like ones based on KiriKiri (GPL!) and DNML (RenPy would be there if it wouldn't use a language like Python in the scripts…). Effectively because I want to be able to play games regardless of what OS or CPU architecture I'm using (examples: {x86_64,aarch64}-linux-musl, Plan9, illumos, …).