Does my long-term payment plan affect my current tax refund?

Yes.  If you have a tax refund for this year, the IRS will generally keep the refund and apply it to your payment plan balance. 

If you are on a payment plan, but are getting a refund for 2024, the IRS will take your 2024 refund and apply it toward the amount you owe from the past year.  You do not have to enter anything on your tax return about that.  The IRS will take care of it automatically and send you a letter a few weeks later.