I'm not sure if this is do to my own inexperience but the /gamerule command on my minecraft doesn't appear to work. I've been trying to make phantoms come back, as well as dying through fall damage, fire and drowning.

I've entered comands like this

/gamerule doInsomnia true

/gamerule drowningDamage true

/gamerule fallDamage true

/gamerule fireDamage true

the text for gamerule doesn't change from red and a list of options doesn't appear for it via tab either. Cheats are on as far as I know and I'm on Java. I'm very frustrated and would appreciate some help.