Defense is trying to be able to ask Hall questions about Floyd's actions that day as well as how Hall interacted with Floyd and drugs himself that day. He is invoking the fifth on these topics. And of course the prosecutor does not want Hall to testify because it shows Floyd was indeed doing drugs and had a history with Hall as supplying drugs. It seems like they want to charge Chauvin and ignore that Hall should be under investigation for Floyd's death because it detracts from their murder charges.

How can one guy (Chauvin) go under a trial while the other involved individual (Hall) can remain without being tried simultaneously? In a way I understand the desire to use the fifth amendment and being able to run trials separately, but it also appears that the defense wants to display that Floyd was certainly on drugs that day and ingesting drugs before and during the arrest.

It appears that the only thing the defense MAY be able to ask is Hall's description of Floyd. Even then, his counsel will likely object.