They are their platforms; so there houses, their rules. They can shadow ban or ban you for no reason if they want to.
Check their terms of service - you'll find that you waived all rights. On the other hand, I'm sure you'll find a lawyer willing to "take a crack at it" so you might as well have a go at suing them. Make sure you have significant, verifiable evidence of the shadowban and can show how it creates tangible harm.