To get SE tax calculated on income that is not automatically added, go to the Sch SE adjustments worksheet. Input on line 6, Other SE non-farm profit or loss.

I do this when I see a 1099-NEC but don't want to add a Schedule C. Some clients don't want a Sch C, but SE tax is required.

Some clients say that they don't have a business, so no Sch C.