Steps to reproduce:
Switch into Survival mode if not in it already
Give yourself any locked raw food item:
/give @s porkchop 1 0 {"item_lock": {"mode": "lock_in_inventory"}} /give @s porkchop 1 0 {"item_lock": {"mode": "lock_in_slot"}}
Use it on a campfire
Observed result:
The locked raw food item is put on the campfire. After some time passes you receive a non-locked cooked food item.
Expected result:
The locked raw food item stays in your inventory.
Can confirm in 1.21.2 Android