One of option is to create new detail based on the same object (Product in Lead). And use this detail in Section wizard.
This is an option but many processes are already connected to the original detail.
I also don't know if any OOTB functionalities are linked to this detail.
Shouldn't there be an option just to disable the multi-select? Maybe going back from this article?
Processes are connected to the Object, but Object remains the same. So, you just create new representation of data.
We use this option if the detail somewhere should be editable, but somewhere read-only. So, we just create 2 details based on one object and use them how we want.
But you can also replace detail schema and override getProductLookupConfig. Probably multiSelect in defined in original one: