Has Christianity been copying most of pagan mythology and then reworking to fit Christianity’s religion? [Spirituality & Religion]

That's an interesting question. It isn't "Christianity" that copies. You're probably asking the question because there are places in the Biblical text where God seems to use worldly customs for His own purposes. You must always remember that He is redeeming and restoring this broken world, so it isn't surprising that He will pick up worldly ideas and customs that are fallen and broken... and redeem and restore them for His purposes. He uses images and ideas that His people can relate to, because they already see them in some way in the world around them.

Can I ask why you asked your question? Are you somehow believing that God should not interact with His Creation... because it has fallen? Or?

You wouldn't be wrong,its an accepted fact that when Christianity first came to Ireland it absorbed and subsumed many differing aspects of the pre existing gods and customs

St Brigid for example never existed but was created from the goddess with bits added on,same as certain festivals eg samhain became all souls night and certain locations such as holy Wells etc where attributed to Christian saints

Idea was that it would be more easily accepted if it felt familiar to them so they basically just re formed the new religion around the old so the pagans would adapt to it.
Early Christian manuscripts created in Ireland during this time included pagan myths and gods associated to them alongside Christian doctrine.I read somewhere the gaeilic story of the tain bo cualigne and other stories from the "ulster cycle" appear in at least two Christian manuscripts

I think it's more subtle and complex than that.

Constantine recognized the power of the message of "Iēsus Nazarēnus, Rēx Iūdaeōrum" to simultaneously unite and then therefore influence a lot of people to a common cause. He was a marketing expert ahead of his time. While promoting early Christianity, he himself waffled and waited until he was near death before becoming baptized. He didn't truly care about religion. He just knew that religion was the easiest way to lead.

He built St. Peter's Basilica and got the ball rolling.

Effectively, over the centuries, Christianity has been used by many world leaders to control the population, using the "word" as a rallying cry to unite. In order to unite, Christianity needed to evolve and become something meaningful.

- the birth of Jesus was likely not in a northern hemisphere winter, so December is very unlikely. But the early Romans tended to celebrate pagan festivals like Saturnalia which ends on Dec 23rd. This allowed for Dec 25th to be a convenient extension of the festival.
- The Celtic cross has a circle in it, which represents the sun. Ancient Celts were pagans who worshipped the sun.
- Haitian Catholics are full of hypocrisy. The Bible says that idolatry is bad, but yet Vodou in Haiti literally uses statues of saints in its rituals.

All of the Christian churches adopt local traditions, but none more than the Catholics. Most of the protestant sects evolved from a sense of, "we like where we are... we don't need to change anymore"

Christians didn’t convert the pagans,
Pagans converted Christianity into paganism

Christian priests were very creative in establishing guilt and fear in uneducated - often poor - individuals.

Always has!
Why try to replace something that already exists when you can subvert it with some clever marketing?

The late Joseph Campbell has a series stating just that. You might find it interesting.

Yes

I've always found the natural world more fulfilling than sitting in church. The old gods are making a comeback, count on it

Beliefs are recycled and local heroes are venerated. If you're looking to connect Christianity to an earlier belief read about Isis and Horus.

No, because nowhere in the Bible is the devil described as having horns! Im sure he doesn't

Christianity has no consistency to it they change their beliefs and create a new branch to it everyday.

Had you considered that it's all connected just told in different ways?

yes. this isn't unknown. they did it to help bring people into the fold.

"copying" is also just how culture evolves.

The Bible story is hardly unique.

Not at all.