Hi¡ I have a big trouble. The first time you play the game , its all perfect but, when you load your last save, all the items double and the game start to get lag. So if you can fix it. Thanks.
(reposting similar information for yourself, sorry)
Unfortunately I do not, and afaik, no one does, know what triggers "New Player bug"
If you dm me on the discord with a savefile and tell me the issue(s) you want fixed/looked at, I can help - in this case I can help clear out the duplicates, restore lost gear and levels (maybe) (and if not, add replacement that makes it like I did) and potentially some other things that may or may not need to be addressed.
Other than recommending the discord route
I would say do the "standard" "failsafe" type "debugging" actions you might do with any game
backup save
Delete the existing Data from the game-folder and local Appdata folder (ShopSim in appdata's "Local" folder), and then redownload the zip and extract it again - I recommend not downloading it to, nor extracting it on/to, the Desktop - I recommend that it be placed somewhere else, and preferably a place where you would assume you have full access to (read, write, rewrite, etc) - as well I often recommend games have their own drive, if you have multiple drives.
and with erased settings, I would often also recommend trying to use windowed mode, with a resolution in game, that matches your desktop resolution, Resulting in a borderless windowed fullscreen looking game, that is hard to tell is windowed. (this is unlikely to be factoring into the issue at hand)