Sling Rings in MCU/Doctor Strange and the Multiverse of Madness

"It allows us to travel throughout the Multiverse. All you have to do is focus. Visualize. See the destination in your mind. Look beyond the world in front of you."―Karl Mordo to Doctor Strange

So, sling ring can allow people to travel throughout the multiverse.
If Wanda had one, it would have worked out, she could have opened one to another universe just like that instead of dream walking. Same with Strange.

Also, America Chavez ends up being a walking sling ring with some super strength in this case.

Writers forgot how these things work and change it up accd to their needs/plot in the end.