It seems I cannot edit my original reply, so I’m posting my edit in another reply. I hope that’s okay. 
You might need to disable Steam Cloud (save syncing) before starting, I did, but I don’t know if that is required. You may also need to launch the game at least once from Steam beforehand but be sure to close it before moving onto the steps below.
If you need to, backup this folder…
C:\Users\gg\Documents\Avalanche Studios\GenerationZero\Saves<>
Delete the “savegame” file in that folder.
Now go to this folder…
C:\Users<>\AppData\Local\Packages\AvalancheStudios.GenerationZero_m0byj0nmrybdr\SystemAppData\wgs\000901F2F457E61A_169E01009F0C4C2D806A18D632ABC594\9184875913C444978F436303B5226266
Note the last two folders might have random digits, and maybe one higher up could too, I do not know for sure.
Copy the newest file in that folder into the \Saves<> folder previously mentioned; that file will have long name with random digits, change the filename to “savegame”. No joke, I launched the game in Steam and saw the CONTINUE option, I clicked it and there was my character with all my stuff! Not only that, but the Steam achievements started rolling in!
A final bit of sweet news, the storage box had the weapons from the Steam bundle I just purchased. Before figuring this out I was tempted to return the game and go back to Game Pass, but this outcome was perfect!