One of the biggest staples in all mainline Pokemon games is that starter critters all have one of three types between Grass, Fire, and Water, and that's something that never changed outside of Pokemon Yellow and Pokemon Let's Go, Pickachu! or Pokemon Let's Go, Eevee!. However iconic it might be to have three starter Pokemon split into those same three types as always, it can also limit the way each of them is designed both aesthetically and gameplay-wise. It's not uncommon for the starter Pokemon to evolve into creatures that either retain their original type with no changes or for them to develop a secondary type that matches their characteristics.
Some dual-type starters get more experimental and unique evolutions, such as Empoleon, Torterra, Delphox, and more. And yet, other combinations are often used multiple times, with one of the most prominent examples being Fire and Fighting, which is the type assigned to three generations of starters in a row with Blaziken, Infernape, and Emboar. Novelty is often praised much more, and it doesn't come as a surprise that some Pokemon fans are seeking alternative type combinations for starters.
The general rule of thumb is that Grass, Fire, and Water types make for great starters because each of them is weak to one of the others and super effective against the remaining one. The perfect trifecta consists of types that do that, but also of types that resist the attacks of those they are super effective against, so Grass is super effective against Water, but it also resists it. A Reddit user by the name of Significant-Permit76 came up with a starter trio that would involve Steel, Fairy, and Fighting types. While it would work in terms of offense, Fighting-type Pokemon don't resist Steel, which breaks the original rule.
However, another Redditor called TheTazaInSpanish shared what the ultimate alternative starter types could be in a Pokemon game, and they would have to be Rock, Fighting, and Flying. Rock is super effective against Flying and resists it, Fighting is super effective against Rock and resists it, and Flying is super effective against Fighting and resists it. The only issue with this trio is that there are few Pokemon with Flying as their primary type, and even fewer that are pure Flying-type, to begin with.
Types aside, starters are a big part in the allure of Pokemon games, as they are the mascottes of sorts for new Generations aside from box art Legendaries. So much so that a gamer built an impressive Pokemon starter-themed gaming PC as a tribute to the initial Pokemon of Generation 1.
Source: Reddit