I hope it's not too big of a deal if I tell you here, but as a massive appreciator of sandbox games myself, I'd recommend looking at Strive: Conquest. Only other adult sandbox I've managed to enjoy.
Talking about other games could be categorized as off-topic discussion, while they are not always removed by moderation, I think it's simply common decency to not add (from the perspective of this game) essentially out-of-context junk to an already 1000 page long forum thread.
However, as a fellow sandbox enjoyer, I understand your necessity to find other good sandbox games. Mentioning some of them is fine I think as long as it doesn't sprawl into a discussion about them.
To keep my post short -as per my reasoning above- here are a few of my personal sandbox suggestions (in no particular order):
- Mad Island
- Era games, such as EraTohoK, but there's an onslaught of them so I'm sure there's atleast 2-3 that one might enjoy
- Strive for Power (since you already mentioned Conquest)
- Artificial Academy 2 and Koikatsu
- Free Cities (modded)
- Masters of Raana
- Portals of Phereon
- Ero Dungeons (not quite sandbox in the same vein as the rest, but still a good game)
I'd rather not post much more. I might make a recommendation thread of my most liked games sometime in the future, which are almost all just sandbox games.
I'd also cheekily mention that I despise how often people tag games as "sandbox" only to find out that it is not sandbox at all, but that's a topic for another day.