I have received an invite to test the new Galaxy 2.0 client but I cannot download an offline installer for the client. I have read thet some people have tried to download the client on Linux to later transfer it to Windows for installation but are blocked (no Linux port of 2.0 client as of yet :-( ). Even though I'm on Windows, I would like to download the client and be able to install it later. Will it be possible in the near future for I would like to test this new client. Thank You.
(If this a repeat request, I'm sorry but I wasn't able to find this topic anywhere)

what do you mean you can not download it? the download button is missing or download is not working? if it is about missing download button (like it happens for Linux users) you can re-enable it by editing inline html for page (addon in your browser, you will have to find button code and remove "disabled" selector from it - gog coders haven't bothered to put more than that, they think Linux users can be stopped by it:)).
if it it's something with the download itself them its another story

I have noticed this too; the installer simply can't be downloaded from Linux.I have installed the regular Gog Galaxy in linux with Lutris using wine. Generally it doesn't work too well but Gwent can be played at least on my machine.
Finally I rebooted into Windows, downloaded the installer and installed it but the same installer is not working in Linux even under wine. It's unable to connect to the Gog servers to be able to download the full installer. I was eager to try it out under wine because it does look promising.

Update:
Well, it looks like Gwent finally stopped working in the old galaxy in Linux too...
But what I did do is try and install Gog Galaxy 2.0 into my Lutris "WineSteam" installation by using the "run exe. inside wineprefix" button and choosing the installer and it finally downloaded the full installer and installed! I did this to be able to connect my steam account too.
The only problem is it still won't start Gwent. But I discovered a workaround for that too. Start Gog Galaxy 2.0, connect your steam account, add Gwent as a non-steam game and it'll start right up. (Gog galaxy has to be running and signed in for this to work.) It's absolutely laughable and bizarre to me that steam starts it up while galaxy doesn't.

Another Update:
Gog Galaxy is running quite smoothly in Lutris but the play button won't start Gwent. However Lutris will start Gwent (create a shortcut pointing to gwent) as long as Gog Galaxy is running. If Gog Galaxy is not running, Gwent will start but eventually tell you you're not signed in. Now I don't need to use Steam to start Gwent.

install winbind

read Lutris FAQ how to properly install games with all required dependencies it needs to run. if you were able to run it with Proton then more likely you failed to install c++, dotnet or DXVK/directX for that prefix you installed it into

Thanks! I'll try that.

Update:
Gog Galaxy is running quite smoothly in Lutris now but the play button won't start Gwent. However Lutris will start Gwent (I created a shortcut pointing to gwent) as long as Gog Galaxy is running. If Gog Galaxy is not running, Gwent will start but eventually say I'm not signed in. Now I don't need to use Steam to start Gwent.