Whoever said that the infinty stones can't be used in the multiverse... they were wrong. They can be

Dude the loki episode, the original comics, and the writers themselves said the infinity stones don't work in other mulitiverse still holds. He will have leave as soon as possible by using stones in that universe.

7573094
well in What If ultron uses the infinity stones and it looks like he's gonna use it to travel through the multiverse

nevermind your right. What If is being generous

True dark strange had his time stone