The thing is that the prohibition against blood is almost entirely in the Old Testament, most of it being part of the levitical laws that Jesus fulfilled.
Indeed, in Mark 7, Jesus declared all foods clean.
And as we can see in 1 Corinthians 8, one of the other prohibitions in the Acts letter—food sacrificed to idols—is not a sin in itself because idols do not actually exist. But Paul says that while it would not be a sin in and of itself, offending your brother who may have weaker faith IS a sin.
Looking into the history of Roman cultic worship/popular religion, strangled meat and food sacrificed to idols and blood were all very popular there. So of course the Apostles would want these new Christians to distance themselves from those practices. Don’t just throw Jesus onto the pile of other gods, but be Christian, a new creation.
Kind of the same way that just showing up to watch a Mormon worship service wouldn’t be a sin, but if someone saw you going into the building, they might get a very bad impression.
Anyways, of course Catholics have transubstantiation wrong, because Jesus refers to drinking the fruit of the vine. But at the same time, Paul says that to take the Lord’s Supper unworthily is to sin against the body AND blood of the Lord—so we know he’s not talking about the body of Christ in the sense of the congregation of believers. (Which is why I believe in the Lutheran understanding of all four being present.)
(And you see, this is the difference between you and me and several of the various FRomans on this thread. I at least bring up counterpoints without namecalling!)
The prohibition against blood was first stated BEFORE the Law, was reiterated IN the Law, and again emphasized by the Holy Spirit at the Council at Jerusalem in Acts 15, when the new covenant was now in effect.
It stands outside the Law.