The biggest problem, of course, is people who read Platonic discourse as genuine history rather than as rhetorical device. But let's pretend anyway.

The first problem is this article's reliance on "the Ancient Egyptian origin story": Ancient Egypt had diverse pantheon with a number of different cosmogonies. While many did share a common element of the land emerging from the ocean, this land being an island then abandoned in a storm is not a common thread by any means. The cosmogony of Amun based at Thebes, for example, commonly held that Thebes itself was the location of that first primordial mound to rise from the ocean. With Thebes as capital for much of the Middle and New Kingdoms, it follows that this particular cosmogeny was a prevailing one.

Where we really run into problems with this particular theory is with its:

virtually unknown, yet well-evidenced theory is that the builders of Newgrange... used boats to transport dozens of huge boulders to the site from Clogherhead... Imagine the quality of boat and level of skill required to load and unload such huge weights, let alone transport them.

The first problem is that 2019 excavations haven't found "boats". They have found a single log boat (seen here) and a number of riverbed anomalies that may be log boats. Either way, these are fairly small vessels of simple construction. Indeed, the head of the UCD research team has said:

While it is highly unlikely that these longboats could have transported large rocks, [archaeologists] think that rafts may have been used.

Although the theory says "It’s not much of a stretch to imagine the wandering Irish sailing from their Atlantic island home to explore the wider world", there is, of course, a very significant stretch between log boats and rafts capable of ~30km of riverine navigation, and ocean-going vessels capable of surviving the ~7,500 miles of Irish Sea, Atlantic Ocean and Mediterranean between Newgrange and Thebes.