I wanted to buy it on GOG to support the devs, but is there confirmation that you can pre-load it before launch? I want to play it on the actual release day. All i've read so far is speculation since Witcher 3 had it.

I don't follow news around Cyberpunk enough to know if there was an official confirmation. However, Thronebreaker, their most recent game, also had pre-load available on GOG, same as Witcher 3. Considering how important the success of Cyberpunk 2077 is to them and how they'd ideally want to sell as much of it as possible on GOG, I think it is safe to assume that Cyberpunk 2077 will also have pre-load enabled.