Hello! Does Quickbooks online support the completion and filing of 1042s forms for non resident contractors?

No it does not.  If the correct box on 1042 S lines up with any box on 1099 you can trick the system and print as if it were 1099 on the 1042S form

Hi! I just processed a non resident alien payroll. I clicked off the non resident box in the employee setup.

I don't see that 30% federal was withheld nor do I see a reminder in the payroll taxes to process the payment for 1042. Did I miss something?

Let me provide some information about a Nonresident alien is a person working in the United States who is not a U.S. citizen, @lstv.

The federal income tax withheld from employees' paychecks depends on their marital status, the number of withholding allowances (exemptions) they claim on Form W-4, pay frequency, and their projected annual income. 

However, QuickBooks Online (QBO)  does not support foreign employees who are not subject to Federal Income Tax Wages (Box 1 on the W-2). 

Here are some resources about the tax set up for foreign employee in QuickBooks Online for reference:

• Exemption status of foreign employees with particular visa types
• Set up Nonresident Alien (NRA) tax withholding for foreign employee

Feel free to get back in touch with me if you have any other concerns with your account and or anything else.  I'll be around to get you taken care of. Keep safe and have a wonderful day!