No Stupid Questions

Not while remaining faithful to their religion. A core tenant of all three faiths you named is that their God (which are all different interpretations of the same god) is the ONLY god and you cannot recognize any other god.

Of course, there have always been varying interpretations of each faith. Christianity, especially, has lent itself to syncretism quite well. There have been (and still are) many cultures where the people would identify themselves as Christian, but see no contradiction in also recognizing aspects of other faiths, including sometimes gods (although they might call them some other word).

If you're following any of the major, world-recognized denominations of Christianity, Judaism, or Islam (eg Catholicism, Protestantism, Sunni Islam, Orthodox Judaism, Shia Islam, etc) then, no, you cannot worship pagan gods. But there are smaller versions of each religion which do.

Ex-Catholic here, standard response where I'm from would be "No, our God is the only god and trying to contact any spirits beside the Holy Spirit just opens you up to all the evil out there".

My understanding is that Abrahamic religions are universally monotheistic and have been since the Babylonian Exile got rid of the henotheistic aspect of Yahwism. Expect to get a lot of pretty convoluted reasoning if you ask a Catholic whether having three persons in the trinity is the same thing as polytheism.

Can a soccer player hold a soccer ball in his hands?

While it's a core belief of Abrahamic monotheist that there is no god but Gods practically speaking some people kept some traditionul/pagan belief. I think obviously about some Africans doing their own mix, but even in Europe, tons of Pagan belief stay around, stuff like knocking on woodor having a Christmas tree, let alone various form of witchcraft which are also illegal for Christians but quite common, no matter whether it's an old man reading runes or a teen girl praying the moon because it looks cool on TikTok

They can do whatever they wish, they were given free will. Should their so-called god not like, it will strike them down or something.

https://en.wikipedia.org/wiki/Thou_shalt_have_no_other_gods_before_me

Only if they don't want to be condemned to hellfire for the blasphemy of monotheism

This really depends on what you mean by "pray."

Sincerely worship and praise a pagan godhead as if they were responsible for the deeds Scripture attributes to God? No. It's as bad as lying in court, stealing, or killing someone.

Falsely go through the motions of pagan prayer, such as in a game, as an actor, or under threat of death? Usually. Some are sticklers, but most are OK with leaving cookies for Santa.

Sincerely giving praise or worship to a being other than God, for things asserted as being done in God's service or things not done by Her? It depends. Some may be hard no, some may be open yes.

There are something like 3 billion nominal followers of the God of Abraham alive today. With such a large population, it'd be hard to find a statement that they all agree on, including "water is wet".

Everyone can pray to what or whomever they like.

Yes. Do whatever the fuck you want.

Should be the same for Christians and Jews, but for Muslims the answer is absolutely not.

You can do whatever you want but in most cultures that isn’t allowed. Depending on how you define pagan gods that is allowed somewhat in east Asia through Shinto deities, Confucian, and ancestors.