Because people keep throwing up variants of this randomly and claiming it's a 'complete list' or some other thing for the last few weeks, I'm throwing up the newest version someone made, with context as to what it is.
This is not official, this is not complete, and we know that some Digimon won't be trainable in the game, some will simply appear.
This is the Digimon we know of (thus far) that will be appearing in the 20th V-Pet, made by a fan.
The Korean text from left to right is (in the forms we'd know them)- Baby/Baby 2, Child, Adult, Perfect, Ultimate, Endurance Mode Opponents
I'll let others list the names.
Based on information from Bandai we know there will be 134 trainable Digimon and 154 Digimon total in the 20th V-Pet.
rastadog77 on Twitter threw up this newest version, with (I believe) fanmade sprites for some, which should be roughly up to date as of 3/24 according to his post.
Thanks to The Golux and DL22003 for bringing it to our attention.