Having just skimmed through the content on said videos, there is no confirmation. Anyone can make a fake Reddit/4chan account and 'leak exclusive info'.
Also, there's at least one continuity error between two of the videos; one claims Galarian Slowbro is Psychic/Poison, and the other claims it's Psychic/Fire. That should say enough about trusting these 'leaks'.
There are multiple forms of Galarian Slowbro: a pure Psychic form that results when you evolve it in regular Galar, a Psychic/Poison form that results when you evolve it in the Isle of Armor mainland, a Psychic/Ghost form that results when you evolve it in the north part of the Isle of Armor, and a Psychic/Fire form that results when you evolve it in the south part of the Isle of Armor.
Galarian Slowking has multiple similar forms: a Psychic/Ice form that results when you evolve it in regular Galar or the Isle of Armor, a Poison/Ghost form that results when you evolve it in the north Crown Tundra, and a Psychic/Ghost form that results when you evolve it in the south Crown Tundra.
(Spirit Aura and Mysterious Stone are new items)
Sorry if this is long.
This is the list of new Pokemon and forms in the Isle of Armor and types, other than the Slowpoke line:
Galarian Wurmple (Bug/Ghost)
Galarian Cascoon (Poison/Psychic) Evolves from male Galarian Wurmple at level 20
Galarian Dustox (Poison/Psychic) Evolves from Galarian Cascoon at level 30 (The levels are alot higher for evolution for the Galarian forms)
Galarian Dustox form 2 (Poison/Ghost) Evolves from Galarian Cascoon if you use a Spirit Aura on it
Galarian Silcoon (Bug/Fairy) Evolves from female Galarian Wurmple at level 20
Galarian Beautifly (Bug/Fairy) Evolves from Galarian Silcoon at level 30
Galarian Beautifly form 2 (Ghost/Dragon) Evolves from Galarian Silcoon if you use a Spirit Aura on it.
Yep, Bug/Ghost becomes Bug/Fairy which becomes Ghost/Dragon.
Galarian Ekans (Water/Poison)
Galarian Arbok (Water/Poison) Evolves from Galarian Ekans at level 23
Galarian Azurill (pure Water)
Galarian Marill (Water/Steel) Unknown evolution method from Galarian Azurill
Galarian Azumarill (Water/Steel) Unk nown evolution method from Galarian Marill
Galarian Nidoran (Poison/Ground)
Galarian Nidorina (Fairy/Ground) Evolves from female Galarian Nidoran at level 22
Galarian Nidoqueen (Fairy/Ground) Evolves from Galarian Nidorina if you use a Moon Stone on it
Galarian Nidoqueen form 2 (Poison/Fighting) Evolves from Galarian Nidorina if you use a Mysterious Stone on it
Galarian Nidorino (Poison/Steel) Evolves from male Galarian Nidoran at level 22
Galarian Nidoking (Poison/Steel) Evolves from Galarian Nidorino if you use a Moon Stone on it
Galarian Nidoking form 2 (Ground/Steel) Evolves from Galarian Nidorino if you use a Mysterious Stone on it
Galarian Shroomish (Fairy/Fighting)
Galarian Breloom (Fairy/Fighting) Evolves from Galarian Shroomish at level 23
Galarian Skiddo (Rock/Ice)
Galarian Gogoat (Rock/Ice) Evolves from Galarian Skiddo at level 32
Galarian Shinx (Poison/Ice)
Galarian Luxio (Poison/Ice) Evolves from Galarian Shinx at level 23 (not 15 as the regular one)
Galarian Luxray (Poison/Ice) Evolves from Galarian Luxio if you use an unknown item on it
Galarian Zangoose (Steel/Electric)
Galarian Tropius (Grass/Fairy)
Galarian Slakoth (Normal/Fighting)
Galarian Vigoroth (???) Unk nown evolution method from Galarian Slakoth
Galarian Slaking (???) Unk nown evolution method from Galarian Vigoroth
Galarian Drowzee (Dark/Psychic)
Galarian Drowzee form 2 (Fairy)
Galarian Hypno (Dark/Psychic) Evolves from Galarian Drowzee at level 25
Galarian Hypno form 2 (Dark/Fairy) Evolves from Galarian Drowzee form 2 at level 25
Galarian Chansey (Grass/Fairy)
Galarian Happiny and Blissey (???)
Galarian Kangaskhan (Normal/Steel)
Galarian Psyduck (Psychic/Water)
Galarian Golduck (Psychic/Flying) Evolves from Galarian Psyduck at level 33
North Sea Shellos (Water)
North Sea Gastrodon (Water/Ice) Evolves from North Sea Shellos at level 30
Galarian Teddiursa (Fairy)
Tummiursa (Fairy) Evolves from Galarian Teddiursa at level 30 (A new Pokemon)
Galarian Phanpy (Ice/Ground)
Woolphan (Ice/Ground) Evolves from Galarian Phanpy at level 30 (A new Pokemon)
Galarian Trubbish (Ground/Poison)
Galarian Garbodor (Ground/Poison) Unk nown evolution method from Galarian Trubbish
Galarian Hoothoot (Psychic/Flying)
Unknown Hoothoot evolution (Psychic/Flying) Evolves from Galarian Hoothoot if you use a Sun Stone on it (maybe "Diurnowl" from "diurnal", the opposite of nocturnal, and "owl")
Galarian Noctowl (Ice/Flying) Evolves from Galarian Hoothoot if you use a Moon Stone on it
Galarian Komala (Grass)
Unknown Komala evolution (Grass/Fighting) Unk nown evolution method from Galarian Komala
Galarian Gligar (Poison)
Coascoar (Poison/Water) Unk nown evolution method from Galarian Gligar
Galarian Dewgong (pure Water) Unk nown evolution method from Seel
Galarian Zubat (Dark)
Galarian Golbat (Dark) Unk nown evolution method from Galarian Zubat
Galarian Crobat (Dark) Unk nown evolution method from Galarian Golbat
Galarian Dratini (???)
Galarian Dragonair (???) Unk nown evolution method from Galarian Dratini
Galarian Dragonite (???) Unk nown evolution method from Galarian Dragonair
Unknown Shellder evolution (???) Have Shellder in your party when you evolve Galarian Slowpoke into Slowbro
Now Zubat and Psyduck appear in every Pokemon region.
Metaleon (Steel) Trade Eevee while holding a Metal Coat
Souleon (Ghost) Trade Eevee while holding a Spirit Aura
Unknown Poison type Eeveelution (Poison) Unk nown evolution method from Eevee
Unknown dragonfly Pokemon (Bug/Dragon)
Tailless Ponyta (Psychic)
Immune form Toxtricity (Electric/Poison)
Gigantamax Rillaboom
Gigantamax Cinderace
Gigantamax Inteleon
Gigantamax Venusaur
Gigantamax Blastoise
Gigantamax (Galarian) Slowbro and Slowking
Gigantamax (Galarian) Golduck
Gigantamax (Galarian) Breloom
Gigantamax (Galarian) Azumarill
Gigantamax (Galarian) Gogoat
Gigantamax (Galarian) Nidoking
Gigantamax (Galarian) Nidoqueen
Gigantamax (Galarian) Arbok
Gigantamax (Galarian) Zangoose
Gigantamax (Galarian) Slaking
Gigantamax (Galarian) Tropius
Gigantamax Raichu
Gigantamax Lycanroc
Gigantamax Kingdra
Gigantamax Zoroark
Giganatamax Gigantamax Donphan (or Woolphan?)
Gigantamax Talonflame
Gigantamx Hydreigon
Gigantamx Drapion
Gigantamax Alakazam
Gigantamax Zsareena
Gigantamx Gyarados
Gigantamx Torkoal
Gigantamxa Hxaorus
Gigantamax Mimikyu
Gigantamax Claydol
Gigantamax Conkeldurr (Sword only)
Gigantamxa Gigalith (Sword only)
Gigantamx Kommo-o (Sword only)
Gigantamx Dusknoir (Shield only)
Gigantamax Froslass (Shield only)
Gigantamax Tyranitar (Shield only)
Gigantamax Stonjourner (and maybe Eiscue too?)
Gigantamax Heatmor (and maybe Durant too?)
Gigantamax Grapploct
Gigantamax Scolipede (Sword only) - Klara's Ace Pokemon
Gigantamx Alakazam (Shield only) - Avery's Ace Pokemon
Gigantamax Sharpedo
Gigantamax Dustxo
Gigantamax Melmetal (already released)
Gigantamax Txotricity (already released)
Gigantamax Jigglypuff
You can get a Gigantamax Jgglypuff from having Smash Bros data on your Nintendo Switch
Kubfu (Fighting) (Pokemon you get at the dojo)
Single Strike Urshifu (Fighting/Dark) Train Kubfu at the Tower of Darkness
Rapid Strike Urshifu (Fighting/Water) Train Kubfu at the Tower of Waters
Lacolo (???) (Sword only) Ent-like Pokemon, probably Grass type
Lacette (???) (Shield only) Ent-like Pokemon, probably Grass type
Lupenor (???) Werewolf Pokemon, probably Dark type
Zarude (Grass/Dark) New Mythical Pokemon
Klara (Poison specialist in Sword)'s team - Galarian Arbok, Poison-type Eeveelution, Toxtricity, Galarian Dustox, Poison Form Galarian Slowbro, Gigantamax Scolipede
Avery (Psychic specialist in Shield)'s team - Galarian Hoothoot evolution, Espeon, Indeedee, Galarian Beautifly, Poison Form Galarian Slowbro, Gigantamax Alakazam