That's because you've overridden the option for Payments & Penalties > 2021 Estimated Tax (1040-ES) > Estimate options [O] with option 3=Greater of 90% of 2021 or 100/110% of 2020 tax.  The one you should select is 2=Lesser of 90% of 2021 or 100/110% of 2020 tax.  I'm assuming you are pretty certain your client will have a lower liability this year.