What is the most damage that can be done in a single melee attack without features that double damage?

I’ve been trying to come up with builds that maximise burst damage recently, but I’m not much of an optimiser, usually preferring themes and/or roleplay.

I’d come up with something along the lines of a Paladin 3/Warlock 5/Bard 12, which could combine Eldritch Smite, Divine Smite and Psychic Blades (assuming College of Whispers) for a total of 9d8+8d6+7 damage (assuming maxed out CHA, Hexblade warlock to use that on the weapon, Dueling Fighting Style from Paladin, a maul as the Pact Weapon, and that Hex had been cast beforehand). This is before I started considering races and other aspects, then that’s when I started to feel out of my depth…

I looked up this question for inspiration: What is the most damage that can be done in a single melee attack?

However, I am disappointed with how many of the answers rely on an Assassin rogue’s Death Strike and/or a Grave Domain cleric’s Path to the Grave feature to double the damage; I mean, don’t get me wrong, they’re good answers, and I’ve even upvoted some of them, but they’re not what I’m looking for today. Given that I do not want to use those routes of doubling damage or getting reliable critical hits via Assassinate, I thought I’d ask the question again, but with a few extra restrictions.

So, what is the most damage that can be done in a single melee attack, within the following restrictions:

  • No features that flat out double damage, so the aforementioned Assassin rogue’s Death Strike and Grave Domain cleric’s Path to the Grave features are considered invalid for this build.
  • Nothing that relies on critical hits, so although it might be interesting to know what the damage would be on a natural 20 as an aside, I otherwise don’t want the build to optimise for critical hits, such as an Assassin rogue’s Assassinate or a Champion fighter’s Improved Critical; hence assume the hit is not a critical hit.
  • No Unearthed Arcana or third party or homebrew; only official 5e material.
  • Multiclassing, feats and Epic Boons are allowed.
  • No help from allies, this should be the damage that can be done by yourself.
  • No polymorph/wild shape, the damage must be by a playable race in its true form.
  • Any class, race, feat, spell or magic item is allowed so long as they are from official 5e material.
  • Assume that the build is for a 20th level character.
  • You can assume infinite convenient luck on things like Wild Magic, but nothing that can be used in an infinite loop to create infinite damage, as that defeats the purpose from my point of view.
  • You can have a round to prepare, so if you needed to cast a spell on the previous turn to set yourself up, that’s fine, so long as it doesn’t have a "flat out double damage" effect like Death Strike, Path to the Grave, etc.