Which shiny variants can a Pokémon transferred from Pokémon Home have?

Question

In Pokémon Sword/Shield, there are two variants of shiny forms which have different types of sparkles:

• Square Sparkles
• Star Sparkles

Yesterday, I received a shiny Pokémon in Pokémon Home through the GTS. The Pokémon had never been transferred into either Sword or Shield (it had the question mark icon and displayed the warning message stating it cannot be moved back into it's original game). I continued to move the Pokémon into my Sword game. After sending it into battle, I noticed the Pokémon had square sparkles.

That got me wondering: Given the separate variants is a new thing in these games, can a shiny Pokémon that's never been transferred into Pokémon Sword/Shield from Pokémon Home have a chance of being either star or square sparkles, or will it always be square sparkles? If it can be either, are the odds the same as if you were encounter one in the wild or are the odds more even?

Answer 1

According to this french site :
https://www.pokebip.com/page/jeuxvideo/dossier_shasse/etoile-8g
If your pokemon originate from go/let's go/event, he will always have the Glistening black (square) effect.
If your pokemon originate from Gen 6/7 (XY and moon/sun), there is a 15/16 chance of having the sparkling white (star) effect (and then 1/16 chance of having the glistening (square) effect).
If your pokemon originate from previous game (rubis/saphire to black/white), there is a 7/8 chance of having the the sparkling white (star) effect (and then 1/8 chance of having the glistening (square) effect).

Considering that the odd in the wild for shield/sword, they are apparently reversed, with a 65521/65536 chances to get the glistening, and a mere 15/65536 chances to get the sparking.