Is there a way to configure upsell to display products at random or from selected categories?
Yes, although it would take some custom development work. If Neto's existing upsell functionality (https://www.netohq.com/support/s/article/cross-sell-products) doesn't suit, it should be possible to modify how you want although I haven't worked directly with this template.
Upsells are controlled by the file \templates\cart\upsell.template.html
It could probably pull in products from other sources like a particular category. You'll definitely need an experienced developer though, this is getting to the more obscure parts of Neto's template system.
