No, if there’s nothing, it’s not using one of the big DRM systems.
There’s a good chance it doesn’t use any DRM, but the only way to know for sure is to install it and try to run it without Steam (rename Steam dir and Steam exe just in case). Some games use Steam DRM or otherwise rely on Steam, so this is to rule those out too.
How do you know if a Steam game is DRM free or not?
How do you install such games without Steam through Linux? Is it just an .exe and you click on it as I haven’t done it since probably the early 00’s?
There is a DRM section on the sidebar of the steam store page that tells you.
Did you mean this? If there is nothing written, does it mean the game is DRM free as if we were on GOG?
No, if there’s nothing, it’s not using one of the big DRM systems.
There’s a good chance it doesn’t use any DRM, but the only way to know for sure is to install it and try to run it without Steam (rename Steam dir and Steam exe just in case). Some games use Steam DRM or otherwise rely on Steam, so this is to rule those out too.