Hmmm, tough one because I'm pretty disillusioned with the procedural generation crutch most of them use so poorly. If you're after the chill vibe of quiet space exploration and a feeling of vastness I'd say elite dangerous was pretty good at making that mechanically interesting. Never tried the latest expansion with the more FPS elements though, so my knowledge there is very dated.

They're not strictly exploration focused but I found the first play through of X4 and Satisfactory to have quite satisfying sci-fi themed exploration. Not much replay value in the exploration of either because the area is hand-made, but the quality of the first playthrough is also much enhanced for that same reason. X4 is an acquired taste, but I suspect you'll adapt to the eurojank controls relatively well and it might appeal to your factorio loving sensibilities. And satisfactory is easy to brute force the exploration by just mass building huge ramps and jetpacking everywhere, but if you just keep it simple and look at the environment more closely you'll find all sorts of hidden goodies and deliberately crafted little platforming puzzles.

If you want the feel of pure space frontier hell and you've never played it, you could try maybe diving into Eve online and banning yourself from all third party knowledge sources and maybe even in-game global chats. Trying to figure everything out yourself might be funny. Or it might just ruin your month(s). 😆