>>50303961The hint is probably Gigantamax Eevee. Chloe’s Eevee’s gimmick is that it is copying Eeveelutions, and her core identity is being indecisive and that you don’t have to change yourself. Chloe is very indecisive, not having a life path or a set goal, and this makes her compatible with Eevee. Chloe and Eevee get power from other people and Pokémon, but they themselves have very little power. They are reflections of the teachings and experiences they went through.
This is an Eevee incapable of evolving, not one that refuses to. She most likely has a Gigantamax. If not, she is clearly a variant Pokemon like Ash’s Rockruff was and could only evolve into a specific Pokémon. But I think the former is more likely. We have yet to see Gigantamax Eevee in the anime.