https://5e.tools/book.html#xdmg,-1
Where is the passage in the 2024 Dungeon Master's Guide that talks about "scale your dungeons"? This is the closest I can find:
https://5e.tools/book.html#xdmg,-1,scaling%20lethality,0
>You can adjust the lethality of your campaign using the encounter-building guidelines in chapter 4. If your players enjoy games that test their characters to the utmost and are prepared to create new characters at a moment's notice, consider using high-difficulty encounters over and over, with little opportunity for rests between encounters, to create a more lethal adventure. Conversely, using only low-difficulty encounters is less likely to lead to character death, especially if characters have ample opportunity to rest during the adventure.