Sorry if someone has already started a thread about this, but are DnDB multiclass rules different than the PHB or am I missing something? I made an example character to illustrate my question:

https://www.dndbeyond.com/profile/Bailius/characters/6929248

Shouldn’t this character have one 6th level spells slot as an 11th level character with two full casting classes? Or am I missing something?

Warnock does not count as "full spellcasting class". The pact magic spell slots are simply added to the ones gained from the bard progression.

https://www.dndbeyond.com/compendium/rules/phb/customization-options#Spellcasting

Ah, thanks for the clarification!