The void glitch effectively triggers the same encounter the Azure Flute does, so if you regard that as legal, then you should consider the void glitch legal as well. serif below is confident you can transfer the Arceus, but as he also implies, it's illegal from a tournament perspective. This Arceus was never 'released' per se.
To get a successful tweak, you need to reach a 'pressure point' in the game's overworld, where different map chunks cross over to each other. You then need to set your Bicycle to a high gear, and ride in a specific pattern over the map intersections, which will cause the game to load nearby map data incorrectly. The most famous location for this is in the middle of Jubilife City, which allows you to tweak into the Poketch Company building and then the void.
This Bulbapedia article explains the patterns that trigger tweaking.
https://bulbapedia.bulbagarden.net/wiki/Tweaking#Patterns
The video showing the Arceus void rollout makes a successful tweak in its opening seconds, which for simplicity's sake, you should aim to replicate exactly -- right down to the precise tile where it opens and closes the Pokedex. The video follows the 12421 pattern on the third bike gear, and later utilises a separate glitch called the Retire glitch which allows you to load the (glitched) Hall of Origin through the void. In short, do exactly what this video does and you will encounter Arceus (see the timestamp 5:05), and safely reach the overworld again.
https://www.youtube.com/watch?v=VrhHXG3cuAw
As an aside, I assume you've used a walk-through-walls hack in the past? Don't use those to enter the void. It does not exploit map data in quite the same way, and is essentially free-roaming which is very risky.
