Minecraft scoreboards: how do I track how many times a player kills another specific player?

So I’m trying to create a scoreboard that tracks the kills of players, but I only want it to increase when they kill a specific player, in this case just the player IGN would do.

I was thinking it would be something like:

/scoreboard objectives add (scoreboardName) minecraft.killed:(player)

but I haven’t got it working.

What command should I use?

Btw this is in 1.16.4