dillite I can find multiple sources of proof that IVs never change, but here is just one:
Individual Values (IVs) – HP, Attack and Defense IVs are, as the name suggests, individual to every single Pokémon and get added onto its base stats to give them a boost. A Pokémon’s IVs are randomly generated when it spawns, hatches or is encountered as a raid boss. IVs cannot currently be modified or influenced, but the higher they are, the more potential the Pokémon has in battle than other Pokémon of the same species. IVs are carried over when a Pokémon is evolved, so always check it’s worth investing the candy into it before evolving (find out how below).
www.google.co.uk/amp/s/pokemongohub.net/post/wiki/ivs-and-their-influence/amp/
IVs only influence a Pokemon’s mathematic stats, so it’s simply not possible for them to change upon evolve (or for any other reason at all). It’s not “what I say”; it’s fact.