Working with Dictionaries - logic seems backward...

[buran]

It's just fine where it is. If you move it inside the else you will need to duplicate it for the if as well. However you need to update the inventory with num_sold, not demand

daily_demands = {
  "pear": [6,4,3,2,1],
  "apple": [5,3,2,1,0],
  "orange": [8,6,5,3,2],
  "lemon": [16,14,11,9,7],
}
 
inventory = {"pear": 21, "apple": 20, "orange": 30, "lemon": 0}
 
for fruit, demands in daily_demands.items():
  for demand in demands:
    if demand > inventory[fruit]:
      num_sold = inventory[fruit]
    else:
      num_sold = demand
    inventory[fruit] -= num_sold # change here
print(inventory)

you can even simplify it

for fruit, demands in daily_demands.items():
  for demand in demands:
    num_sold = min(demand, inventory[fruit]) # change here
    inventory[fruit] -= num_sold

or

for fruit, demands in daily_demands.items():
  for demand in demands:
    inventory[fruit] -= min(demand, inventory[fruit]) # change here