Shall we talk about female first party characters then?
Toadette has risen up the ranks in recent years through Captain Toad, New Super Mario Bros, Odyssey and Mario Maker 2 she's become both a canon mainline cast member and the defacto player 4 of the series.
Let's not forget the internet losing their mind when she introduced the concept of Peachette too even if that was more squarely aimed at Bowser.
Pauline is currently being marketed to advertise Mario Kart Tour and was heavily leaned on for Mario Odyssey's advertising to the point I thought she was going to have a FAR bigger role than what she actually got. She was also the biggest Mario Tennis Aces DLC reveal so she's becoming somewhat of a "Superstar" in her own rights.
Dixie Kong is the first character I think of when I think Nintendo heroine. Not Peach, nor Zelda, nor Samus even. Dixie has been one of the very few Ninty girls to NOT get kidnapped through the years and unlike Samus there's no twist that she's a girl, she wears it on her sleeve.
Impa is one of the few reoccurring Zelda characters and has garnered fan support through...well mostly Hyrule Warriors if I'm honest.
Still she is undeniably a fierce warrior and with the focus in Zelda being Sheikah based in recent years it seems Impa is one of the more logical options if Zelda is ever allowed a newcomer.
Midna is currently an assist trophy but despite that she is easily one of the most popular fan favourite characters in all of Zelda, rivalling that of Skull Kid at the very top. She's also remained a popular choice for Smash speculation despite her game being far from the most recent entry.
Tetra is another ridiculously popular female character in the Zelda franchise although her fandom has quietened down a fraction just due to not wanting to add another
to the limited Zelda pool.
There's a few other good options for female Zelda cast members outside the above such as Urbosa, Fi, Mipha, Ruto, Medli, Marin, Lana, Maron and Epona the freaking horse even, etc. Zelda is very much a goldmine for those seeking some fun female options.
We got Octoling who as discussed previously has a whole heap of options available to them as Inkling cannot quite portray everything from the game, and whilst there's now an Octoling Boy meaning we'd likely get both genders, the Splatoon community were begging for Octolings to become playable based entirely off Splatoon 1's Octoling girl enemies. Heck, the female characters are very much the default in Splatoon.
Then we have Elma who is capable of duel wielding blades, guns and riding in a freaking mecha as well as some other more spoilery abilities that we're not going to go into right now.
There's also Fiora and Pyra and Mythra but since I've played neither of those Xenoblades I feel unqualified to talk about them.
Springman, whilst the face of ARMS is far less popular than female fighters Twintelle and Minmin and Ribbon Girl is arguably as big a face as he is of the franchise seeing as how they both appear on the boxart and are the first fighters we meet.
You have traditionally more feminine Pokemon choices that have lasted the test of time with Gardevoir(who can still be male) and Eevee(who is far more likely to be male but insanely popular with female trainers from what I can tell).
I also find it INCREDIBLY ironic that whilst we ended up with Incineroar and everyone was predicting Decidueye would be the Pokemon newcomer when Ultimate was first announced, that the seemingly ignored other starter evolution; the feminine Primarina, was
voted by Pokemon fans in Japan as THE most popular final evolution stage of the three ranking in as the third most popular Sun and Moon Pokemon. Rowlet was number one, but neither Decidueye nor Incineroar made the list.
Whilst Bandana Waddle Dee is inarguably the most popular Kirby choice, Adeleine managed to maintain fan interest despite not appearing for basically 18 years. Her reveal in Star Allies on Switch was a big deal to Kirby fans, and with the ability to paint minions and fight with them she has an almost unlimited potential moveset wise for Smash.
Fire Emblem! Yes, not everyone's favourite choice for a Nintendo newcomer, but between Byleth and Edelgard being the two most likely Fire Emblem candidates right now alongside Lyndis being the most popular Fire Emblem character(bar maybe Ike) and even Anna making ground between being Three Houses DLC and being a driving force in the mobile runaway success that is Fire Emblem Heroes, we have a handful of yet more perfectly great female options that make sense, and that's ignoring other great candidates that offer something new like the face of the manakete's Tiki, the insanely popular wyvern rider Camilla, or magic wielders Celica, Tharja and Micaiah. Much like Zelda there's an absolute treasure trove of female options here.
Akira Howard/Officer Howard comes in both male and female flavours and Astral Chain has a frankly insane amount of cool moveset potential between five different legions, dual character combat and the X Baton.
Nintendo really does seem to have some fantastic options for female characters that are currently being utterly ignored n discussion due to the Third Party hype train mowing down any discussion of some of these homegrown favourites.