4. Was his son a clone?
In the galaxy of Star Wars, parentage can come through a number of ways. One of those is the exact replication of a person via cloning. As the architect of the clone army the Republic used in The Clone Wars, Sheev Palpatine would be well aware of the opportunities that cloning allows — and have the access to make use of them.
The clones that made up the army were genetically modified, aging faster than the normal human and largely being more receptive to orders. That being said we know that the cloners of Kamino are not closed to taking special requests, as the template for the clone army, Jango Fett, requested an unaltered clone of his own. He raised this boy as Boba Fett, adopting him as his son.
If Palpatine wanted a child without the entanglements of a mother, he could have cloned himself. This would have provided an heir if one were needed, or another host body if he discovered a way to transfer his consciousness from one body to another — perhaps what he did after his death in Return of the Jedi, perhaps not.
It also could have served as an experiment of sorts: would a clone of a powerful Force user be likewise strong in the Force? Do midi-chlorians transfer perfectly through the cloning process? If his son was a clone, then clearly Palpatine’s strength in the Force was passed on by his son, if his son did not bear the same strength himself.
There are some other options for Palpatine’s parentage other than the two already listed, but they range further afield and are less likely given the statements in The Rise of Skywalker about Rey possessing Palpatine’s power. Adoption, surrogacy, etc are likely off the table.
The way Rey’s relationship to Palpatine is referenced makes it unlikely her father was a clone. If she was the biological child of a clone of Palpatine, wouldn’t she more accurately be his “daughter” in relation to his Force powers? While two steps removed from Emperor Palpatine, she was only one step removed from his exact genetic copy.
However unlikely it is certainly a possibility that Palpatine cloned himself and raised that clone as his son. Until we know for sure it stays on the table as an option, if one that raises some interesting ethical questions about parentage.