All effects last 1 tick, making them broken, but instant health and damage still works (it looks like it works only when executed in command block, idk). You can also make a repeating command block with /effect command and it still kinda works (when used blindness, screen may be flashing)

How to reproduce:
1. /effect @p minecraft:regeneration 60 1
2. Look at inventory; no effects
3. /effect @p minecraft:instant_damage 200 126
4. you didn't die