The criteria are: you either play as a faction with a unitary consciousness (whether organic or robotic), or you're the only one in your faction who is sentient (e.g. you command animals, zombies, golems, robots, elementals etc.) It should be turn-based or at least pausable. The ones I'm aware of:

Stellaris
Warhammer 40K: Gladius: Tyranids DLC
Uh... SimAnt?

Oh, and when it comes to playing a hive mind, feel free to recommend other genres too, especially RPGs.

lol, almost any necromancer faction will do then?

I belief playing as the Necrons should suit you too then ;)

Or as the Borg in Star Trek, though only available on board i belief

Nope, I'm not terribly familiar with WH40K lore but I'm pretty sure Necrons have individuality, certainly the lords do. But yes, the Borg would qualify for this afaik. As for necromancer factions, keep in mind there has to be no more than one character with human-like intelligence. So, say, the Scourge in Warcraft 3 is right out.

Starcraft's zerg campaign. Brood wars & starcraft 2's heart of the swarm expansion if you don't mind a figurehead (possible spoilers for SC1)

I expected someone would bring up Starcraft. Granted, it's been 15+ years since I so much as looked at a Starcraft game, but I distinctly remember the celebrates. If it was just the Overmind, then it would qualify. But maybe it's different in Brood War or SC2.

Maybe R-type Command?

Although, I think the concept of the Bydo campaign is more along the lines that you/your army from the earth campaign got captured and assimilated into the Bydo but still have some sense of sanity/self awareness. ...Just not enough to understand what's actually going on or why their allies are attacking them as they try to return to earth.

They're working towards a prime goal though. The only other thing I had in mind is Sarfifice

Edit: Darwinia/multiwinia | Total Annihilation/Supreme Commander

The Hive - https://store.steampowered.com/app/325730/The_Hive/

blurb: "The Hive is an RTS RPG single player game where you assume control of insectoid hive mind, and explore the vast underworld on your journey to the surface."

Grey Goo, the Goo faction. Without going into spoilers, I think that would fit the criteria.

Pretty sure one of the factions in Sword of the Stars is hive minded. Can't remember which.

yea, that much is true, their lords do have their own individuality but, according to your own reasoning where you include Tyranidds then necrons could be oke too. there have been multiple hive fleets ( you see ;) )

There is rumor, at least in my understanding of the warhammer lore that all the current hive fleets that have decimated the galaxy are parts of maybe a bigger fleet that may or may not control everything from one entity but the larger tyranids also have some influence on their lesser spawn, not to mention the different hive fleets that are more or less under autonomous control even when directed by this theoritezied super hive mind.

there are many battle reports indicating how tyranid attacks will grow in force and strenght during the duration of the battle starting out as attacks done by mindless creatures that over the course of defeat evolve, with the help of larger tyranidss into a calculated menace

so you either accept a couple of flaws or remove the tyranid faction from your list :p

Despite it being advertised thematically as the opposite, Majesty is an RTS where you can't control the individual units; you only can give incentives in various ways. The result is that it feels like they're just mindless parts of your hive mind; so mindless that you can't give them specific orders.

Undead Horde maybe. As a necromancer you can order your army to attack in a specified direction or retreat back to you. It's a rather simple, but fun game. I've enjoyed it more than a I expected.

Empires of the Undergrowth - haven't played this one yet, but it might be something to your liking.

Fair points, but since you play as one hive in Gladius, it still counts.

Hmm, i'm not sure how it is with the necrons, are the agents considered lords.. i guess so right

If you would have asked for 2 enjoyable sci fi minded 4x games i would have shared with you shadow empire and the new meta skirmish mode with a purpose in aow planetfall but, since neither games actually have a hive minded faction .....