According to Microsoft support for Windows 10 officially stops on Oct 14, 2025.

SteamOS might be one of the better solutions for the Steam client since Microsoft and all other corpos will drop the support for Windows 10 in a near future anyway.

Right now I am learning and try to figure out if it's possible to install this SteamOS as a second operation system and make it possible to switch between this and the first one.

I am not a big fan of telemetry and forcing updates so I don't consider Windows 10 as a better solution in this regard. Though the better comparability with Windows games is somehow tempting.

Yes, it is.

HOLO ISO is pretty much the SteamOS with better hardware support and easier intallation. Not all hardware is supported and last time I've tried, nVidia was a no go.

With that said, I don't see Microsoft breaking compatibility any time soon and even if older games stop run on Windows 11, I'm sure there will be some sort of workaround, even a VM with a older Windows version.

The bigger issue is stated on earlier posts, will GOG's offline installers break compatiblity as well?

You may want to adjust the expectations a little.
I don't know the goal of the project (if there's one) but I downloaded the current stable version 0.4.14 one year ago and 0.4.13 in 2020. Things are very slow and it looks like a personal project(quite interesting though), whenever it will be realeased, will probably be outdated...

If the galaxy.dll starts requiring APIs that do not work on Windows 7 and those games require that .dll and those games are updated then compatibility will be broken.

Options would be:
Revert to older version if you have it.
Hope that a wrapper exists to allow that functionality (vxkex or similar)
Hope that a GOG Galaxy emulator doesn't require newer than Windows 7.

Best solution is to get GOG to require pubs/dev to make existing and new games not require that .dll to operate which may be difficult if those games were coded to depend on functionality that those games require. If other stores don't have that requirement it just means GOG is more of a hassle to devs.

I wonder if this is covered by Valve's promise to let customers continue to have access to their games in the event that the Steam network is discontinued, seeing as this move will make a bunch of games that don't run on Windows 10 and 11 inoperable given as they'll no longer be able to be verified through Steam on older Windows.

I beg to differ. Most of the innovation and experimentation was on PC. Consoles had copycat after copycat and were basically low power arcade machines. If you noticed, all best genres now running on consoles, started on PC.
Now, if you personally liked console games better it's another story.

Really, that's pretty vague. How about we get specific.

So uh, Mario was kind of a genre defining thing was it not? How about Zelda? Ever hear of Metroid or Castlevania? How about the entire fighting game genre, Metal Gear, Resident Evil, Final Fantasy and the rest of the JRPG genre, Souls games, it's an endless list of mega popular titles.

PC was basically fist person shooters, some sims, strategy games, CRPGs, and point n click adventures. Some of these did well but there was not the volume of big selling titles on PC.

How about GOTY stuff leading up to Steam?

1988: Double Dragon, Mega Man 2
1989: Mario 3
1991: Maybe Sonic
1992: Surely Street Fighter 2
1993: Mortal Kombat
1994: Donkey Kong Country
1995: Twisted Metal, DKC2
1996: Mario 64
1997: Golden Eye 007, FF7
1998: Ocarina of Time
1999: Soulcalibur
2000: Tony Hawk's Pro Skater 2
2001: Halo, Metal Gear Solid 2: Sons Of Liberty
2002: Metroid Prime, Grand Theft Auto: Vice City

PC had none of that at launch & just did not have the volume of AAA franchises console did until after Steam was a success.

I was talking about genres. I don't care about the single games you like. Again, most popular genres of today started on PC.

People don't play genres. They play games. You've yet to name one.

Uh, like the last GOTY Elden Ring? That genre started on console.

I think Blade of Darkness for Windows was out WAY before Demon Souls and all of those other Souls-likes.

Check King's Field on PSX. 1994

True. FromSoftware has been at it for a while.

Miyazaki was highly influenced by the Wizardry series.

Looks like I'll have to migrate my old laptop to Linux (aiming for Zorin OS) sooner rather than later. It currently runs on Windows 8 (not 8.1) and has plenty of issues, so I was gonna have to make the switch either way, but I was hoping I could at least wait until I could afford to switch out the mechanical drive for an SSD so I don't have to install twice. Oh well. I've been meaning to do a dive into Linux systems anyways, since I'm hoping that by the time Microsoft drops Windows 10, maybe GOG Galaxy and most of my other games and software will run on Linux.