Lately, I've seen the Youtuber "Kwebbelkop" playing a mini-golf game which is basically Golf With Your Friends, but its UI is slightly different. Observable in the video below of this other game being played, is this Golf With Your Friends with some sort of UI mod, or is it a totally different game?
No it is not Golf With Your Friends. It took some digging, but I'm confident in saying this is the Minigolf game in the game Tower Unite (see the second video on the scroll bar in Steam. Its called Minigolf, and is the game seen in the Kwebbelkop's video). Steam's description of Tower Unite is:
Tower Unite is a community-based virtual world party game with online games, entertainment, activities, and no microtransactions.
It's actually a collection of games in one, sort of like Mario Party.
The way I can tell that its this game is through the video on Steam. The UI is the same as seen in the video in the question, the names next to the balls are off to the side just like in the video, and it has a similar overall look. Another give away is when Kwebbelkop's gets his Hole in One in the beginning of his video, the words "Hole in One" pop up. In the video on Steam, a hole in one occurs at around 30 seconds in, and the words look exactly the same.
It looks like some of the other games included are some sort of zombie outbreak looking game (sort of like infection on Halo?), and some sort of hamster ball race game, and a bunch of other ones.
The game is currently in Early Access on Steam.