I have specified in the backend under Upsell and Cross-sell that more than 100 products may be visible, but it only displays max 12. I hope you guys can fix it.
The option in Theme Settings is designed for the standard predefined single product page without using the layout builder. Since you are using the single product layout builder, the corresponding settings for the number of products need to be adjusted in the respective Products (grid or carousel) element responsible for displaying upsell products (screenshot https://monosnap.com/file/w2mvfP7IDpNJMhmkco22aKWc3vYUOS)