What is the highest theoretically possible shiny chance in any game?

Question

excluding guaranteed shiny raids and stuff like that.

Answer 1

The highest intended shiny-odds in a mainline Pokémon game are found in Pokémon Ultra Sun and Ultra Moon's Ultra Warp Rides. After having caught all possible legendaries found in a particular 3-ring "blooming" wormhole, said wormholes will have a 36% to contain a Shiny Pokemon after travelling 5000 or more light years.

Source

Comments

What about shiny charm, something similar to sandwhiches, or location? Not that I know the first thing about usum but are there any factors like that involved in "Warp Rides"?

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The chance for a shiny are set for non Legendaries/UBs in Ultra Warp Rides, so they aren't affected by the Shiny Charm