I have 33 current builds on D&D Beyond for BG3. Only 2 are single class. Of the others, most only do a level or 2 dip in a second class. Also most will have to wait for modding, because they include subclasses/ races not in the PBH. Here's some that can be played, as soon as multiclassing is added:
Red Priestess- Regular Human Hermit Light Domain Cleric 8/ Evoker 2
https://www.dndbeyond.com/profile/Merlex/characters/30474510Battle Mage- Githyanki Sage Eldritch Knight 6/ Abjurer 4
https://www.dndbeyond.com/profile/Merlex/characters/30339003Divine Trickster- Regular Human Acolyte Rogue 1/ Trickery Cleric 9
https://www.dndbeyond.com/profile/Merlex/characters/30474519Slayer- Wood Elf Outlander Hunter Ranger 4/ Champion Fighter 6 (using the UA Class Features Variant for Rangers)
https://www.dndbeyond.com/profile/Merlex/characters/30474682Ninja*- Variant Human Criminal Assassin 3/ Shadow Monk 7
https://www.dndbeyond.com/profile/Merlex/characters/30474773Fist of the Forest- Wood Elf Hermit Land Druid (forest) 4/ Open Hand Monk 6
https://www.dndbeyond.com/profile/Merlex/characters/30793556Archmage- Half Drow Sage Dragonic Bloodline (Red) Sorcerer 8/ Evoker 2
https://www.dndbeyond.com/profile/Merlex/characters/30474213Prophet*- Variant Human Sage Knowledge Cleric 1/ Diviner 9
https://www.dndbeyond.com/profile/Merlex/characters/28068032The Ghost*- Variant Human Charlatan Arcane Trickster 3/ Illusionist 7
https://www.dndbeyond.com/profile/Merlex/characters/30133245Edited to add: *Ninja, Prophet, and The Ghost require that Variant Humans be in the game.
2nd Edit: Was missing the link to my Prophet build.
Here's my version of Vic's Abjurer/ Warlock:
Witchblade- Tiefling Sage Abjurer 8/ Hexblade Warlock 2
https://www.dndbeyond.com/profile/Merlex/characters/28060087I don't take Eldritch Blast, not going to hit much with a 14 Charisma. This build (my favorite btw) relies on enemies damaging themselves. I take Devil's Sight and Armor of Shadows as my invocations. Use Darkness (spell and Tiefling feature). Flaming Sphere + Booming Blade. Fire Shield, Armor of Agathys. Hex and Hexblade's Curse (no save on either). I use Shield, Absorb Elements, Protection From Evil/ Good, Counter Spell, Dispel Magic, Banishment, Stoneskin and Armor of Shadows to keep Arcane Ward up.
