As I suspected, I figured someone had a list of all non-homebrew subclasses so far (released by WoTC)
Giant in the Playground had them:
Spoiler: Barbarian
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Path of the Ancestral Guardian (XGtE p.9)
Path of the Battlerager (SCAG p.121)
Path of the Berserker (PHB p.49)
Path of the Storm Herald (XGtE p.10)
Path of the Totem Warrior* (PHB p.50)
Path of the Zealot (XGtE p.11)
*Elk and Tiger totems (SCAG p.121)
Spoiler: Bard
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College of Glamour (XGtE p.14)
College of Lore (PHB p.54)
College of Satire (
UA: Kits of Old)
College of Swords (XGtE p.15)
College of Valor (PHB p.55)
College of Whispers (XGtE p.16)
Spoiler: Cleric
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Arcana Domain (SCAG p.125)
City Domain (
UA: Modern Magic)
Death Domain (DMG p.96)
Forge Domain (XGtE p.18)
Grave Domain (XGtE p.19)
Knowledge Domain (PHB p.59)
Life Domain (PHB p.60)
Light Domain (PHB p.60)
Nature Domain (PHB p.61)
Protection Domain (
UA: Cleric: Divine Domains)
Tempest Domain (PHB p.62)
Trickery Domain (PHB p.62)
War Domain (PHB p.63)
Spoiler: Druid
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Circle of Dreams (XGtE p.22)
Circle of the Land (PHB p.68)
Circle of the Moon (PHB p.69)
Circle of the Shepherd (XGtE p.23)
Circle of Spores (
UA: Three Subclasses)
Circle of Twilight (
UA: Druid Circles and Wild Shape)
Spoiler: Fighter
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Arcane Archer (XGtE p.28)
Banneret/Purple Dragon Knight (SCAG p.128)
Battle Master (PHB p.73)
Brute (
UA: Three Subclasses)
Cavalier (XGtE p.30)
Champion (PHB p.72)
Eldritch Knight (PHB p.74)
Knight (
UA: Fighter: Martial Archetypes)
Samurai (XGtE p.31)
Sharpshooter (
UA: Fighter: Martial Archetypes)
Spoiler: Monk
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Way of the Drunken Master (XGtE p.33)
Way of the Four Elements (PHB p.80)
Way of the Kensei (XGtE p.34)
Way of the Long Death (SCAG p.130)
Way of the Open Hand (PHB p.79)
Way of Shadow (PHB p.80)
Way of the Sun Soul (SCAG p.131, XGtE p.35)
Way of Tranquility (
UA: Monk: Monastic Traditions)
Spoiler: Paladin
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Oath of the Ancients (PHB p.86)
Oath of Conquest (XGtE p.37)
Oath of the Crown (SCAG p.132)
Oath of Devotion (PHB p.85)
Oath of Redemption (XGtE p.38)
Oath of Treachery (
UA: Paladin: Sacred Oaths)
Oath of Vengeance (PHB p.87)
Oathbreaker (DMG p.97)
Spoiler: Ranger
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Beast Master (PHB p.93)
Gloom Stalker* (XGtE p.41)
Horizon Walker (XGtE p.42)
Hunter (PHB p.93)
Monster Slayer (XGtE p.43)
Primeval Guardian (
UA: Ranger and Rogue)
*Renamed from Deep Stalker
Spoiler: Rogue
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Arcane Trickster (PHB p.97)
Assassin (PHB p.97)
Inquisitive (XGtE p.45)
Mastermind (SCAG p.135, XGtE p.46)
Scout (XGtE p.47)
Swashbuckler (SCAG p.135, XGtE p.47)
Thief (PHB p.97)
Spoiler: Sorcerer
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Divine Soul* (XGtE p.50)
Draconic Bloodline (PHB p.102)
Phoenix Sorcery (
UA: Sorcery)
Sea Sorcery (
UA: Sorcery)
Shadow Magic† (XGtE p.50)
Stone Sorcery (
UA: Sorcery)
Storm Sorcery‡ (SCAG p.137, XGtE p.51)
Wild Magic (PHB p.103)
*Renamed from Favored Soul
†Renamed from Shadow
‡Renamed from Storm
Spoiler: Warlock
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The Archfey (PHB p.108)
The Celestial* (XGtE p.54)
The Fiend (PHB p.109)
Ghost in the Machine (
UA: Modern Magic)
The Great Old One (PHB p.109)
The Hexblade (XGtE p.55)
The Raven Queen (
UA: Warlock and Wizard)
The Seeker (
UA: The Faithful)
The Undying (SCAG p.139)
*Renamed from The Undying Light
Spoiler: Wizard
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Artificer* (
UA: Eberron)
Bladesinging (SCAG p.141)
Lore Mastery (
UA: Warlock and Wizard)
School of Abjuration (PHB p.115)
School of Conjuration (PHB p.116)
School of Divination (PHB p.116)
School of Enchantment (PHB p.117)
School of Evocation (PHB p.117)
School of Illusion (PHB p.118)
School of Invention (
UA: Three Subclasses)
School of Necromancy (PHB p.118)
School of Transmutation (PHB p.119)
Technomancy (
UA: Modern Magic)
Theurgy (
UA: Wizard Revisited)
War Magic (XGtE p.59)
So that's 102 official subclasses. Official meaning "released by the WotC design team and not homebrew"
EDIT: more than that, since that's an old thread and doesn't include recent ones like the Rune Knight