Nice to have you in the Community again. I can help with why a vendor is not showing up to print a 1099 for.
A vendor can be missing when preparing 1099's for a few reasons, such as how their payments are tracked. I'm including an article that covers troubleshooting steps for this form in QuickBooks Online: 1099 Troubleshooting. I recommend looking in particular at the section, 1099 vendor is not showing on the list when preparing 1099's.
I'm confident this resources will aid you in generating this form for your vendor.
Should you have any questions, don't hesitate to post them below. Warmest regards.