Box 16 on my schedule K-1 is checked, but the Schedule K-3 has no foreign countries in Line A, so turbotax won't let me file. should I just say Box 16 isn't checked?

Most forms K-2 and K-3 forms do not need to be filed this year.

The IRS announced on Tuesday February 15, 2022 that most K2/K3 reporting for 2021 can be delayed until the 2022 tax return filing.

This is an extract of the IRS announcement:

The IRS intends to provide certain additional transition relief for this year from the Schedule K-2 and K-3 reporting for certain domestic partnerships and S corporations with no foreign activities, foreign partners or shareholders, and without knowledge of partner or shareholder need for information on items of international relevance. For 2021, these qualifying domestic partnerships and S corporations will not have to file the new schedules. We are taking this step in response to feedback we received from the tax community and our stakeholders.  The IRS will provide full details of this relief soon.

If the partnership has no foreign activities, you can uncheck box 16 and e-file your return.