question regarding the lore because extremly confused here

[TheMightyMollusk]

The planet in question isn't even referred to as a planet. It is called a star. The role Hydaelyn and Zodiark play on this star is all explained in the ShB MSQ.

In archaic usage, any significantly large celestial body is called a star, including planets. This isn't an error, just an old and now-uncommon use of terminology.

[Floortank]

You'll need to progress the MSQ. Without giving too much away, the world we play on is actually called 'The Source'.

It is called the Source, sure, but that's not its name. Whatever the Ascians called it before all the summoning went down is unclear.

The planet in question isn't even referred to as a planet. It is called a star. The role Hydaelyn and Zodiark play on this star is all explained in the ShB MSQ.

This is just poetic license. Ancient peoples would refer to most heavenly bodies as stars. This included planets. It's why Venus is called "Morning Star."

You'll notice a lot of archaic language used in FFXIV for poetic license, and to create immersion. "Hydaelyn" or "the Source" is still a planet. We have even seen a SE produced globe of Hydaelyn.

[Enkidoh]

The actual name of the world we play on, as far back in history that we know, is "The Source". Our world is colloquially called "Hydaelyn" by the general populace because of the goddess (aka primal) Hydaelyn.
Yes, the world existed before Hydaelyn, and it would have had a different name before the splintering, but currently it's called Hydaelyn.

Yes... and no.

The use of the term 'the Source' is in reference to what was left of the original planet after the Sundering, and hence it's almost always only refered in that way when talking about dimensional travel and it's place in the dimensional cosmology with it's Shards, and then only by a handful of people who actually know about the concept (specifically, the Scions/Archons and, presumedly, Sharlayan) - almost everyone else on the world calls it Hydaelyn, and this has been the case since 1.0.

Interestingly, as far as I was aware there is no indication of anyone on the First calling their Shard 'Hydaelyn' - apart from Ardbert and his friends it's unclear if anyone there even is aware of Hydaelyn the goddess. And from little we've seen, the Ancients pre Terminus/Sundering seemed to have no name at all for the original world, it was simply called 'the Star'.

And then you have Norvrandt's equivelant of Lake Silvertear also being called 'The Source' which only adds further confusion into the mix. And to say nothing of SE themselves confusing the matter back in 1.0 when Eorzea and Hydaelyn were used interchangably for the name of the world the game takes place in (rather like the Ivalice games like FFXII being wildly vague about whether Ivalice was a country, a continent or a world).

As for the 'star' thing, that's a result of Japanese phonetics with the words for planet and star being the same thing and so there is no distinction (it's actually quite common in a lot of translated anime and manga to use the word 'star' in the context of a world).

The use of 'star' to describe the planet in English is therefore just a quirk of localization (the English version being developed hand in glove with the Japanese version). It might seem odd to a modern English speaker who knows the difference between a star which is a giant ball of glowing gas and plasma undergoing nuclear fusion, and a planet that is a satellite of said ball of a gas, and that the later is in English what our world physically is in real life, but it also does show this is not our world and thus things are different there - it's all part of worldbuilding.