Isekai isn't new though. I'd say it's as old as anime, but the truth is it's far older than that. Person or persons going off to another world through means magical or divine or technological is as old as writing itself.
So are you really sick of the concept, or sick of the repetition of similar themes (usually video game systems and menus existing in said other world)?
Do you go all the way back to ERB with his Princess of Mars and other books in the series and have an issue with a man running around on a fantasy version of mars going on adventures? Probably not as much because the setting is very different than the very generic fantasy settings modern Isekai keep using.
I believe what you're actually sick of is the repetition of similar concepts and themes, rather than the concept of a person or persons going off to another world or dimension or whatever via one means or another.