Hello currlyfriies, sorry to hear this about your save files.
Is there any way Geforce Now could be saving your game elsewhere?
Here is where you can usually find your saves - Documents\Anno 1800\Accounts\\\BarnabySmudge1.A7S (Example)
Can you try turning off cloud save synchronizing in the Ubisoft Connect menu, then trying to manually save in the game and locate your new save in the location gave above? Please get back to me and let me know once you have tried this.
I would also advise reaching out to Geforce Now about this directly here as well, as the cloud save synch issue seems to occasionally come up -
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