Bard at level 20 gains Superior Inspiration, meaning they get one paltry inspiration back if they roll initiative with none. It seems quite possible this will never come into play in many games, even.
(They also get a second 7th level spell slot, but any multiclass full caster gets that too.)
It seems one is always better off taking a level of any other full caster instead (Sorcerer should at least be always possible assuming amicable DM, but a Bard probably has 13 Int or Wis for Wizard/Cleric/Druid too), or even a level of any class which gives you anything at level 1.
The reason I am asking: I definitely want at least level 17 for actual 9th level spells. Then level 18 Magical Secrets (cough Wish cough) seems to give more value than any level 3 multiclass pick. Level 19 gives ASI/feat, also perhaps worth more than any 2nd level multiclass. But level 20, is that supposed to be a capstone ability?
Is there any reason at all to become a level 20 Bard? Some rule about class level 20 I am missing? Something related to Epic Boons? Some rare magic item for level 20 bards only? Anything?