Yeah it's gone from my library too. This is really not a good sign. When did GOG start doing this?
Probably at the same time they partnered with Epic and allowed games with aspects of DRM to be sold here. Roughly when a blue announced something along those lines: "We allow developers now to create their content as they see fit, in order for them to distribute it through our expanding store". cannot remember thread name. It was meant as a reply to some of the voiced concerns for DRMed games finding their way here, i think... Gog started doing many weird things, nobody should ever feel safe for their library, anymore.
Besides, people warn that new installers have incorporated Galaxy elements that cause various inconveniences, telemetry etc. Older threads here with very old users, adviced people to back up installers as soon as you bought them, at that very instant at that. Well, that was the best piece of advice somebody could ever give. I myself was too relaxed and trusting on Gog, so i naturally neglected that. Couldn't foresee they would slowly rot away and become the exact opposite of what they once stood for. My nick was for joke or trolling purposes, back when i created this account; today, it unfortunately fully represents my sentiments exactly, alas.