If you set doMobSpawning to false and use the kill command, it will display "Killed X entites" (X means the number of entities) including the player. However, if you explore in unloaded chunks, mobs can spawn even if the gamerule doMobSpawning is false. I did type doMobSpawning "correctly" due to the arguements Java Edition are case sensitive.

How to Reproduce
1. Create Infinite world type
2. Type/click suggested rule name

 /gamerule doMobSpawning 

3. Type

 /kill @e 

4. Respawn and explore unloaded chunks.