In this case I think that the mystery of life requires something to avoid existential angst, and some people use the afterlife as that something. Other religions (like Buddhism) might view the entire question of “what is this?” as absurd, and so use methods like meditation to help alleviate the angst, thus avoiding absurd beliefs.

TLDR: the mystery isn’t the absurdity but our reaction to it might be absurd.

Buddhism has plenty of "absurd" beliefs of this sort. If anything, the delineation of "absurd" is anything but simple.

Yeah some sects can get whacky. I think the core Buddhist tenets are pretty much absurdity free but I agree that it’s not simple to determine.

Are there any beliefs in particular you were thinking of?

The six realms of existence, hungry ghosts (pretas), siddhi, sacca-kiriya, the cosmic buddhas, the Pure Lands...