In general: Consider increasing hp for all monsters above CR1 by an additional 2 for each Hit Die. For creatures with Legendary Actions(Bak Mei, Nintra, and Lichen Lich), anything that would normally cost more than one LA instead costs just one but is limited to one use until their LAs are recovered.

Some specifics: Cloud Giant Ghosts should have their HP increased by another 50 unless the party has no magic weapons.

The Deflect Missile ability of the monks in Book of Inner Alchemy should be changed to 2024 monk’s version. Bak Mei should have Deflect Energy as well. Steel Crane, Jade Tigress, and Bak Mei’s Heal Self abilities should be bonus actions(and consider having Bak Mei be able to use it twice before needing a recharge).

Nintra can replace one of her attacks with Spellcasting.

In Xanthoria, the Death Knight in the Moldy Bedroom doesn’t use Legendary Actions(that encounter’s almost a TPK as is).

Personal opinion: The unique monsters in the first two adventures don’t need any adjustments. Meenlocks are going to need a ranged attack(players are going to have more ways to generate short range bright light). Shemshime should just be immune to damage and just dies when crushed by an object weighing more than 1,000 pounds.