Gantz, Imawa no Kuni no Alice (OVA) Recommendations
Not sure if Alice in Borderland or another season of Gantz with a little less "alien"! Both are a roller coaster ride of action, struggle for survival, drama, starring Unknown-being-thing toying with people and main character who is having an existential crisis due to feeling useless and helpless.
Both force the characters to play a deadly game of survival.
The Characters enter another world and have to adapt to that world by playing the games to survive and eventually escape.
Both main characters get sent to a place where they have to play a deadly game to survive.
LIterally the same setting with main characters having to play numerous games of survival.
only difference is that the main character have different personalities and also in gantz, the fighting is more physical whilst in Imawa no Kuni no Alice the survival aspect is done using thinking and solving puzzles though in both animes fighting and puzzle solving aspect are featured.
Imawa no Kuni no Alice has people participate in a game where they are fighting for their life. Both have great action scenes and lots of mind breaking content. (Imawa no Kuni no Alice is incomplete so I'd suggest the manga instead.)