Simple RAW 3

[Arkhios]

Q355: I am a player character currently at zero hit points and I am rolling for death saving throws. By whatever turn of events, I acquire some temporary hit points whilst downed. What happens?

(We couldn't find a clear answer, so we ruled it as 'you get the thp and you don't roll for death saves until you lose them, but you still can't take actions')

A355 You still make death saving throws, for you aren't stable.

lf you have 0 hit points, receiving temporary hit points doesn't restore you to consciousness or stabilize you. They can still absorb damage directed at you while you're in that state, but only true healing can save you.

In other words, temporary hit points for someone at 0 hit points may prevent an automatic death saving throw failure from taking damage.