Do u need to place the PKM you capture on your team to show it or just finish register it in PokeDex and it will automatic complete when u choose the option YES
You need to have all the images under encounters in the menu be colored.
You can achieve that by capturing, evolving and stealing.
You also don't need the exact regional form. For example: You can have a normal normal Growlithe only and the Mt. Chimney Hisuian Growlithe will be counted as an encounter you have, even though they have different entries in the in game Pokedex.
Probably a bug tho, so it might be removed in the next version.