I have come across similar questions like Can I swap my cantrips known for new ones from scrolls?, and Can a spellbook contain cantrips?, but I noticed that the questions predate Tasha's Cauldron of Everything, and only one answer makes a reference to the optional 3rd level rule.
For reference (P.75):
Cantrip Formulas: You have scribed a set of arcane formulas in your spellbook that you can use to formulate a cantrip in your mind. Whenever you finish a long rest and consult those formulas in your spellbook, you can replace one wizard cantrip you know with another cantrip from the wizard spell list.
Copying a Spell into the Book. When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it.
Copying that spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote it. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation.
What I would like to know is if this creates the opening for wizards to increase their cantrips known through spell scrolls with the same methods and rules as would apply to other wizard spells, or if there is some reference I missed negating such a concept. I understand that it refers to first-level spells or higher, though from what I understood, this was because until Tasha's Cauldron of Everything was released, cantrips were actually not written down in spell books at all, only memorized. But now the Cantrips Formula seems to have changed that bit of lore.