The only isekai x sport I can think of is the baseball one. Which is pretty good if u haven’t read that.
I think made-up sports are too hard to do. Even Keijo is really just wrestling with special rules. Made-up board games, on the other hand, seems far more common. They had one in Hunter x Hunter (ant arc), Love is War had a few (thanks to Fujiwara and board game club), and Sket-dance had them. Many gambling mangas also have their own board or card games.
I’ve read the whole thing, but skimmed most of the later chapters. I’m afraid it doesn’t get much better. Compared to Ranma and Inuyasha, it is much much much more episodic. There are no arcs and rarely any long stories that span more than 1-2 chapters. The stories become very repetitive too given how long the series lasted. The story does develop but it’s very slow.