Hello GOG staff and fellow forumgoers, i was wondering if the free update will also come to GOG (given that a lot of games have not received such updates on GOG but have on Steam)?

Why shouldn't it come? All other updates and bugfixes for Cuphead have arrived here right on time.

Moreover, the official announcement refers to "PC versions" (plural) and says that it's coming to "everyone who owns Cuphead on any platform". I don't see any reason to speculate that it won't be released on GOG.

It seems there was a update today, but no changelog.

There is a changelog on the devs' website.

http://studiomdhr
.com/cuphead-is-coming-to-nintendo-switch-plus-new-free-content-for-everyone/

That isn't exactly a changelog though, but an advertisement of the main new features. The single bugfixes aren't listed there, e.g. controller support has improved a lot, but it isn't mentioned.