This is a long shot since I have only vague memories of it, but:
A game from probably the early 2010s. It was 3D, (probably) free to play, and was played with a client downloaded on the PC. It was a strategy (RTS?)-type scifi game that had you building on planets with… probably some larger scale space stuff with spaceships and invading planets and whatnot. I think it was a MMO.
I have only — again — vague memories of briefly playing it. It sort of makes me think of Supreme Commander? I kind of remember putting down power plants, maybe. There might have been some kind of designer section to the game with some degree of customization to units and/or buildings?
I don’t believe you had any kind of physical avatar or character in the game world.
I highly doubt it’s still a thing today, by virtue of what I remember of its scale and the fact that I probably haven’t heard of it since. Feels like the kind of game I would have heard about since then if it’s still going.
Importantly, it was not Shores of Hazeron. I know this sounds like it’s Shores of Hazeron to anyone familiar with it, but it definitely was a different game.
That being said, it’s been almost definitely over a decade since I briefly played this game and I’m sure the memories of it have been corrupted by memories of other games. So if anything else seems even somewhat similar to even one part of the description, it could be it.
Yep, I do remember something very much similar to what you have described. Can't remember the name tho, sorry. It's much older than 2015. Actually was trying to find it like 15Y ago by myself and failed. It was already dead then, i suppose. What i do remember of it: 100% MMO, persistent world, "space" as in there was more than one planet, with ships that transported resources. Also mining. There was tons of little mines owned by players all over the (starting?) planets. That's all. This is gonna be one hell of a thing to dig up

Also, I have request of my own. Maybe someone remembers something like god-game, where you indirectly control small tribe of prehistoric peeps that strive to survive? I do remember playing a demo or very early access of it, probably on steam, like 5Y ago, but can't find any trace of it on my PC/whishlists/etc. It did have 3d graphics, in vaguely similar to astroneer style. Demo progressed as far as to get some basics like well and, i guess, temple of sorts, and then getting your first newborn peep. Any ideas?