I just got a steam deck.
How compatible are the GOG games?
Will the gog galaxy be compatible with the steam deck?

GOG hasn't announced anything w.r.t. steam deck, but what they have shown is a relative lack of concern for Linux. So assume the answer is no.

Here's a couple of days old thread about that:
https://www.gog.com/forum/general/making_gog_compatible_with_steam_deck

Rest assured that while CDPR/GOG may be content to rest on the Laurels and Hardee's while the world passed them by, Valve has no such qualms and even if intentionally or otherwise, they will be making as may titles as capable on running on the deck as humanely possible.

Here are two easy things:
1) Dobox is Dosbox, it'll run no matter what since there's a native version. This even includes games which inexplicably have Windows only installers but are pure DOS.
2) ScummVM is ScummVM, it also has a native version.

Now the less easy things:
3) Most 2D indie games should run fine via Proton. Especially games that draw to things like the SimpleDirectLayer.
4) Many games have source ports which are coded to natively run on any system. Such as OpenTTD, OpenRCT2, and eDuke.

Harder things:
5) 3D accelerated games are going to be a gamble. You'd think Serious Sam 1 would run as free as it gets, but it doesn't know what the hell Vulkan is. And for games that were made during the protocol wars, GOOD LUCK.
6) 32 bit library support is being taken out of many distributions or retired; which means that some games just aren't going to work right. There's even a few games here on GOG that are distributed with broken library files. There are many factors including an irreversible bug which make it simpler to retire these instead of keep supporting them.

I understand that there's ways, but it's honestly more of a hassle than using Steam, which is a shame. I got Heroic Games Launcher working, and it did sync my GOG account, but the only game that even starts so far is Heroes 3.

Still, Heroes 3 on the go is pretty neat.

That's normal for most older games as Vulkan wasn't released until 2016. Serious Sam FE & SE support OpenGL though. Go to \scripts folder and edit PersistentSymbols.ini. Edit the line persistent extern INDEX sam_iGfxAPI=(INDEX)0; and change it from 1 (for DirectX8) to 0 (for OpenGL). Do you have a list of ones planning to do that? That's an unbelievably dumb decision that sounds like it will break most PC games made between 1995-2015.

That's not true. On the contrary: when steam deck first came out, GOG announced that GOG will not be supporting it.

There are even articles in the gaming press about that very statement from GOG.

Well, the steps are already being initialized in many distros. And many of them are already dropping i686 CPU support or have already junked it, this is just a logical next step.

As for specifics, It's a little hard to figure out how to phrase it to modern search engines. Even the Archwiki refers to 32-bit packages as legacy.

You're talking about the tweet right?

https://twitter.com/GOGcom/status/1495670845334822912

"There's no official support" is not the same as "there will be no official support." The tweet is merely stating the (obvious) state of affairs and does not announce any future (non-)plans. And support is not the same as compatibility, which is what the OP asked about.

A bunch of "press" just turned that tweet into "will not": https://www.gamespot.com/articles/gog-will-not-offer-official-steam-deck-support/1100-6500919/ https://techraptor.net/gaming/news/there-will-be-no-official-gog-steam-deck-support etcetra

I can't be bothered to look for a source but I think at some point GOG said or implied Galaxy would be available for Linux too. I don't believe that anymore, but assuming they followed up on that, chances are it "would be compatible" with steam deck whether GOG supports that platform in official capacity or not. EDIT: I looked up anyway, at least the wishlist item for linux release of galaxy was "in progress" for years; now it no longer is though. https://www.gog.com/wishlist/galaxy/release_the_gog_galaxy_client_for_linux And near the download button it originally said something like "Also available for Mac OSX and soon for Linux"

EDIT2: blue claiming there will be linux support eventually: https://www.gog.com/forum/general/gog_galaxy_client_closed_alpha/post27

I don't have a list but Ubuntu announced they will drop 32bit libraries right after Apple did it. It caused a massive burst with people who used Ubuntu to play games, as you know it Steam still runs on 32bit.
If I'm not mistaken Ubuntu did drop most of the libraries and so did most of Ubuntu derivatives, like Mint, PopOS, Mx, Elementary and KDE Neon.

https://itsfoss.com/ubuntu-19-10-drops-32-bit-support

Edit: Have some Linux Iso's on the HDD for use or just because they are interesting, and Ubuntu Iso grown from 1.8GB on 18.04 version to 3.5GB on 22.04.

as argued elsewhere -gOg and Valve are not competing on hardware, but on software.

if people buy the Steam Deck, then that is just another piece of hardware to run your software. the question then becomes: where do they, or should they, buy the software from?

edit - no, i think the reason why is that the Deck is Linux based

same thing with me i have steam deck but how can join with GOG

might also reply to this. Valve has had some hits an misses . The Valve Index is arguably the best VR headset in the low-medium pricerange, and it is doing quite well.

The Deck sold out as soon it was ready, and you need to be on a waiting list now if you want to get one, so it is doing well as well, and it is getting decent reviews.

the cconcole they tried to make.... not so succesful

The Steam controller got good reviews and sold well but that was discontinued rather surprisingly.

So I would say they are 50/50 at hardware, however Steamdeck is in a decent position however competition in the handheld pc market is growing exponentially so it comes down to if they can keep pace.