Juries are not supposed to answer questions of law, they are supposed to answer questions of fact. The way it's supposed to work is that they are told X, Y and Z are the things required to commit this crime, here's the evidence - do you believe the evidence presented is compelling enough that you are convinced beyond a reasonable doubt that X, Y and Z are the case here?
but then was unmovable in finding the dude innocent because of this opinion then that'd be an issue.
Not guilty, rather than innocent. The distinction is relevant because not guilty just means that they could not be proved guilty beyond a reasonable doubt to the jury. There is such a thing as a finding of innocence in some (but not remotely all or even most) jurisdictions, but it's much much
MUCH harder to obtain. You essentially have to know it exists in your jurisdiction, actively pursue it, and then prove that you could not possibly have committed the crime beyond a reasonable doubt. Louis Gonzalez III went through that process regarding the allegation of rape against him and succeeded largely because he had an extremely thorough and well corroborated alibi that meant it was physically impossible that he could have done what he was accused of, unless he's secretly the Flash.
Who was so under a rock that they never formed an opinion on police brutality, black lives and racial history in America?
Why you should never be a juror. You aren't supposed to be trying racial history or the value of black lives, you are supposed to be deciding if the evidence presented causes you to believe beyond a reasonable doubt that Chauvin's actions that day met the definition of second-degree unintentional murder, third degree murder and/or second-degree manslaughter as defined by the relevant laws.
That's why things like being caught lying about involvement with BLM or for example talking about the need to get onto juries as a form of activism to promote your ideal of racial justice might potentially be used as ammo to argue the trial was unfair. Or for another completely unrelated example, if people were to make a display that appears to threaten a defense witness and the jury wasn't sequestered it might be argued that the jury were aware of said threat and might have felt threatened into deciding a certain way as a consequence.
Side note: The juror in question has done an interview:
https://getuperica.com/334572/listen-black-juror-in-derek-chauvin-trial-speaks-out-exclusive/
...I realize it's not a popular vote affair. I was mentioning that even discounting this guy, it was still an 11-0. That's not nothing.
Retrying over and over again to try and hit the statistical impossibility of finding the 12 people in the country who A) haven't developed a strong opinion on this case and B) wouldn't be convinced it was murder after watching a nine minute video of a murder is ludicrous.
Think of it like a construction code for a boiler or other dangerous machinery - there are i's you have to dot and t's you have to cross to meet code and if you fuck it up you have to scrap it and start over, even if the thing built outside code was just as fit for purpose as the one built to code. If that juror had some kind of serious bias directly related to the case that he lied about, then it might very well be decided that the trial doesn't count and you have to start over, even if the result is very likely to be another guilty verdict.