Rotom heat has microwave disc

Volkner’s ancestor sells them to you and he calls them Mechanical *insert item*z His dialogue implies that he doesn’t know their function but realizes it’s something special

Because it (indirectly) produces heat

I see. Thanks.
I guess they must've fallen through the space-time holes as well.

Yup, Arceus gives zero fucks about the stability of spacetime because it's all a part of its Grand Plan, same reason Porygon's allowed to exist almost a century before it was invented.

Porygon only exists inside the space-time bubble, and ofc if you bring it out. The fact that we can't find it in the future until it's created is proof enough that they did not became invasive or simply did not procreate in PLA.

Well of course, there's no Ditto in Hisui, and the species presumably died out from having no compatible technology to keep it alive properly.
But it's still a preordained move considering you literally cannot challenge Arceus until you have everything on the Porygon Line, never mind the Pokedex having slots for them in the first place, and it begs the question of how no one's pointed out any odd similarities in the process of Porygon's development now that, retroactively, there DOES exist information on the species before it was ever made properly.

Still heats up your food and it's not like there's radiation type.

On the bright side, that'll make it very easy for later games to explain why Hisui Pokemon are suddenly alive again. "This fucking bear thing popped up after my Porygon disappeared"

it's because chronologically this is the first time it's happened. previous games in the series didn't have Porygon line in the Hisui Dex because Arceus porting back the protag hadn't happened at that time

because the only thing it heats up water

more like it hadn't happened in that dimension

PLA is the "first time" these events are playing out because it's a timeloop, bucko. The whole point of PLA is how Ancient Hisui finds its starting foundation to become Modern Sinnoh, and the protagonist is integral to this process.
Arceus has willed it so that without the game's events, the Pokemon World as we knew it starting from Red and Green fundamentally could NOT have turned out the way it did because of how significant and tied to the gods the story is, and the unknown possibility of one of the antagonists wielding that power for the worse, or Giratina being a bastard and trying to go Demiurge on the Pokemon World without the PLA Protagonist to get it to chill out.
If the PLA Protagonist isn't sent back to Hisui even if the point in time they come from "doesn't exist" yet, the PLA Protagonist might not even be born to get sent back and ensure they shift history as per Arceus' design, and in turn, secure their own existence.
And since we're dealing with events caused by Arceus, a truly Absolute Creator God that is above all of the concepts that have come into place AFTER it was born, it's thus only logical to now wonder if Porygon's inventors are going to note the similarities in appearance, naming and other conventions matching up to a mysterious species loosely documented in Hisui's time.

Do we even know anything about porygons creators. As far as i know the most we know is that it comes from a computer program

That’s all we know, developed by Silph Co.

The most we have is that it was developed in Cinnabar's Lab with heavy involvement from Silph Co.