According to the Roman Catholic Church, is halal meat being offered up to idols? For it seemed good to the Holy Spirit, and to us, to lay upon you no greater burden than these necessary things: that ye abstain from things sacrificed to idols, and from blood, and from things strangled, and from fornication; from which if ye keep yourselves, it shall be well with you. Fare ye well. (Acts 15:28–29, ASV)
No, but the sacrifices of pagans are offered to demons, not to God, and I do not want you to be participants with demons. (1 Corinthians 10:20, NIV)

In some nations there are Muslims working in the slaughterhouses blessing the meat so it becomes halal meat, so that Muslims can eat it when it is sold in the stores.
For many this is  not okay. What does the Roman Catholic Church say about this? Is this meat being offered up to idols?
The Roman Catholic Church does not teach that food certified by either the appropriate Jewish authorities as meeting requirements for Kosher certification, or by Islamic authorities as meeting requirements for Halal certification are foods offered to idols. The Catholic position is that the God of the Jews and the God of Muslims is the same God as the Christian God,, and therefore not an idol.

In explaining different understandings between most Jews and most Muslims, from the understanding that most Christians have of God, Catholics teach that Jews and Muslims,  and frankly many non-Catholic Christians,  too, have (at best) an incomplete knowledge of the nature of God.