If you deleted the content the authorities have no evidence a crime was committed other than one witness saying “yes, totes CSAM”. They’re not going to be able to pursue the uploaders on that alone, and reporting it will only draw attention to yourself. If it was me I’d shut down or lock down the server and move on.

By law, you are not liable.

There are hundreds or thousands of different jurisdictions in the world. I don’t think you can say this confidently unless you know exactly where OPs server is located.

I expected to open this thread and see 30 recommendations for stardew valley but I don’t see any. So stardew valley.