since 1.6 came out you can no longer use mods.
unfortunately GOG Galaxy updated my game and i cant seem to make it downgrade it back to 1.5

is there a way to download the old offline install of 1.5?

It was possible for awhile under "Manage installation" -> "Configure" -> "INSTALLATION" tab and then uncheck "Automatically update to newest version"

But now there is only older 1.6 versions.

I am lucky i still have my 1.5 offline installer files. And it was possible also for awhile to download the 1.5 offline installers when downgrading under extras.

If you want to keep old versions, you will have to download the offline installers.

Thats true for ALL GoG games.

I certainly wished it was otherwise. Really would love to own the latest No Man's Sky 3.x, before they completely changed it.



P.s.: Oh and you will be able to use mods again, the mods will just have to update.

And as a rule, I NEVER change game version while I'm in a walkthrough. Saves a lot of headaches.