New update after two months of silence (their coder was on well deserved vacation) was dropped today, yet nothing on GOG.
That happend often during Saturdays & Fridays and I thnk GOG might have problems with working hours.

This is a very common thing with GOG. Steam's system of pushing updates is automated whereas GOG someone has to manually do it. Negative being you have to wait longer for an update but positive being usually the updates won't break the game. It is what it is.

Edit: I'm not sure if it's different depending on if the title is in development or not. Maybe someone with more knowledge on the subject can answer that.

Actually, I don't think new update has been released yet. They only released "newsletter" of sorts that they are now back to full staff and what they are working on for the update. They are pretty active on their discord, and yet this is the last post from their #game-updates channel (see attached image). Their steam update thread has the same information.

Only for offline installers... Galaxy has tools to automate patches.

But of course, at the end of the day it's on devs or publishers to use them.