As of 1.16-ish, Read-Only objectives such as Health cannot have players assigned to them since you cannot add or set any values.

This has probably been reported already, but couldn't find it.

Affects health, xp, level, food, air, armor: https://minecraft.gamepedia.com/Scoreboard

1) scoreboard objectives add h health
2) scoreboard players set @p h 0 (impossible, read-only)
scoreboard players add @p h 0 (impossible, read-only)
3) scoreboard players list @p (No objectives shown)

I expect entities to be able to be added to the "h" objective. Before, players were added automatically, but now they're not, so these objectives are inaccessible.