Non steam games wise, Myself and my friends play mindustry an RTS tower defense like game. It has a stupid amount of upgrading and building and conquering new areaa with new enemy's. I too also love scrap mechanic I JUST WANT THE BIG UPDATE DANG NABBIT!!!
If your into terminal/hacker like games id highly recommend duskers. Its a game where you control salvage drones and go onto abandoned space crafts and thered enemys and you close and open doors with terminals and stuff. And your drones have upgrades and abilitys for certain things like traps and activating turrets. I also lovr the graphics very analog Its a really great game if your into it.
Also slay the princess is a really well write single player narrative. And is like old school choose your Adventure with a horror element. I have sunk many hours since the pristine cut droped
All of these games are available for gog