Is the demon named Moloch that is mentioned in Leviticus 18:21 and Acts 7:43 really just Satan ?

all worship of false gods is demon worship according to Paul.

1 Cor 10:19 What do I mean then? That a thing sacrificed to idols is anything, or that an idol is anything? 20 No, but I say that the things which the Gentiles sacrifice, they sacrifice to demons and not to God; and I do not want you to become sharers in demons.

Satan is the king/head/prince of demons. Paul says it is 'demons" plural that are being worshiped. Your question seems to be about selecting which one is being worshiped in the case of a given false god. I don't see anywhere in scripture where it is mapped out.

Certainly you can say that either directly or indirectly Satan is being worshiped

After Babel , elohim were put as lords over all nations but they too rebelled.. God later took the House of Israel and the 'promised land ' for Himself among these other nations. . Satan simply means adversarial/adversary, so yes any of the rebellious elohim are considered satans, just like Peter was.

According to Psalm 95 v. 5 in the Septuagint, which corresponds with Psalm 96 v. 5 in the Masoretic, the gods of the gentiles are demons. The MT says “idols.” Both are correct - since the gentiles worshipped idols of demons.

In His epistle to the church in Pergamon included in the Apocalypse (Revelation) Christ our God referred to the city as having the throne of Satan, likely a reference to the Pergamon Altar, a massive sacrificial altar, which in antiquity would have been a horrifying place, flowing with the blood of victims (the verses in question are Revelation 2:12-13). There were a few other Pagan centers of worship in Pergamon which our Lord might have been referring to.

It is clear if we examine heathen religions that the vast majority are at least accidentally diabolatrous - in the case of Islam for example Allah has evil properties, Hinduism with Shiva and Shiva’s avatar Kali being another very blatant case, whereas in other cases the false religions promote self-worship which is the sin that caused Satan’s downfall; self-worship is something we Christians must avoid by refusing vanity.