Like WooCommerce, MultiVendorX is also not compatible with the core concept of multisite. This means, when you install and activate the MultiVendorX plugin, it will be activated on all sites, and there will be an option to create a store, set up products for each site on the multisite, individually. Each store will be independent of the other.
So, say I have 3 sites in a multisite- Blue, Orange and Purple (with Purple being the main site). When I install and activate MultiVendorX on Purple, it will be activated on Blue and Orange as well. When I add products on Purple, or update some settings the changes will not be reflected on Blue or Orange, by default.
