payment of estimated taxes is voluntary.
since you are expecting your 2022 income to be down the safe harbor for avoiding penalties is you need timely estimate payments and withholding equal to 90% of your 2022 tax (the tax rules if you have a state income tax will be different)
if you had the desktop software I would suggest once you complete the 2021 return and e-file it (this is to prevent efiling the wrong return) you open and save the file as say "2022 estimate" then you can adjust the figures any way you want to see what's needed for 2022. I would give myself some cushion
for online you can use the 2021 capital gain worksheet, print it out, and revise the numbers to match what's expected in 2022. double-check that your calculations are correct. then bump it up a little to give yourself some cushion.
