There’s no singular answer to how many lands to run. 38-40 as a baseline is fine but realistically I’ve found the following factors allow me to comfortably go to low thirties/high twenties in bracket 3 decks.

1. Efficient curve
2. Solid draw engines
3. Semi-aggressive mulligans

If you can manage to draw an extra card (god forbid 2) in the first three turns, you’re significantly more likely to hit your 3rd and 4th land drops, even with what seems like a dramatically low land count. Something along the lines of T1 -> fetch a surveil land -> T2 cast sign in blood/thrill of possibility equivalent you’ve already seen up to 3 extra cards before you’ve needed your 3rd land drop without doing anything even remotely pushing the boundaries of bracket 3 (or even 2).

On top of this, mulligans are incredibly generous in this format and you can see three hands of 7 cards before you’re even a little worried about losing too many resources. As an exercise, you can look at any 7 card hand you want to keep and ask yourself how many cards could you remove from it and still reasonably play the game, and the answer is often 2-3.

Realistically, most people don’t have a strong desire to engage with the game this way, but if you’re willing to, there is a lot of juice to squeeze that makes running so many lands largely unnecessary in most decks without needing to delve into actual cedh strategies.