There's a lot to be concerned about in 2020, and among those concerns, though perhaps not right at the top of them, is Doom Eternal's lack of deathmatch. But there is hope for us: Goat of Duty, a deathmatch FPS starring goats (that's why it's called "Goat of Duty"), is free-to-keep for a limited time.
Grab it between now and April 1, and you'll get to keep the Early Access title forever (it's usually $10 / £9 / AU$16). Steam reviews are sitting on a "very positive", and I'd hazard a guess that the servers will be quite busy for a while at least, now that it costs nothing.
Goat of Duty launched into Early Access last July, and judging by recent Steam missives it looks like there's a substantial update around the corner. The focus is on a fairly stripped back deathmatch experience (with goats): "No nonsense: no need to master a convoluted metagame, learn different characters, combine skills, strategic team play... just devilish combat arenas, powerful weapons, and fast-paced action." And goats.