PLO50 call or fold vs 3bet et call OOP ?

Fold preflop. This type of hand has very rough playability and being in worst position in multiway pot is not going to make it easy to play. Think about flops that you are happy to play in likely 4way pot. Unless you hit basically top two with fd or better it wont be that great. Low sets are dangerous in multiway single raised pots. If you flop fd you often dont have support with it which also means that playing it OOP is tough.

As played Im not sure about call versus 3bet. Probably losing play.

I fully understand that this is an ev- call vs squeeze.
I would like to know about the cold call in SB vs CO open. Would you have defended this hand in SB or is it just a fold? What if i was on the button?

Yeah I meant with fold preflop to fold right away. Even without BU flat call I would fold. If we are BU versus CO open I would still fold usually. It does help if blinds are very tight but even then it's very marginal at best imo.

I would call with hand like A554ss though (A high suit).

Depending on how aggressive he is I might call SB too. But it needs to be a maniac with 60%+ range and overaggressive Postflop. Otherwise I fold too