A 4th quarter estimate should have been made by 1/15/21 so you can either make a late payment now or pay by 4/15 with a tax return.
If you don't pay the estimates and your withholding isn't any of the following you could be hit with underpayment penalties.
1) 2020 balance due after withholding is less than $1000
2) withholding covers 90% of 2020 tax
3) withholding is 100% (110% if 2019 adjusted gross income is over $150,000) of 2019 tax