I see from previous posts that online was only between GOG Galaxy clients, but that they may add crossplay with steam later.

It's been later now. Is there crossplay yet?

seconding this question! My friends have the Steam version, but if crossplay is working I'll get the GOG version for sure.

I have never seen any mention of crossplay ever coming to SOR4 and would be astounded if so.

Can you link something to verifying your claim?

Bit of a necropost but I hadn’t found if it was implemented or not, can anyone confirm?

Crossplay requires an additional account external to the store, and so able to deal with all the others.

For example the game "Dying Light" makes you register to a Techland account (their development studio) for that.

There is no such account in SOR4.