This has (apparently, I can't check it myself) been fixed in the Steam version via official update #1 released on Friday. The update doesn't seem to have arrived here at GOG yet.

That's great, but I don't wanna rebuy it though. The update better arrive here soon, or ND should allow us to refund.

I'm not suggesting re-buying it, just saying to give it a little time. GOG tends to be slower to update than Steam, because GOG staff have to put in effort to create the offline installers for download and then test it on their various test machines before uploading it to the server for download. (Steam just allows the devs to upload new files and they are downloaded via the Steam client automatically).

Also, it has been known for GOG not to get the updated files at the same time as Steam, which isn't good, but it can mean further delays. So give it a few days first. Also, the devs have been replying to people on the Steam discussion forums for the game, so maybe asking there when the update is coming to GOG will helpfully remind them that there are paying customers here that are still waiting (if indeed they haven't given the updated files to GOG).

Note that there is also a beta version patch available on Steam, so it could be that Night Dive are waiting for that to go live before giving the updated files to GOG, to save everyone here from updating twice.

Enemy speed may be out of whack, but it is still tied to the difficulty setting. Why not just turn the difficulty down until the patch is up?

Unfortunately you will have to stick to normal for the time being while the enemy speed is fixed. It is still faster than the original, but much easier to swallow since you are using a mouse and keyboard to compensate for that.