From the instructions for Form 8949, which flows to Schedule D:
"The holding period for short-term capital gains and losses is generally 1 year or less. ... The holding period for long-term capital gains and losses is generally more than 1 year. ... To figure the holding period, begin counting on the day after you received the property and include the day you disposed of it." (https://www.irs.gov/pub/irs-pdf/i8949.pdf
So the way I read it, you would exclude 4/20/2020, and include 4/21/2021 in the counting if you sold today. 4/21/2020 to 4/21/2021 seems to me to be one day more than one year and thus long term, but I wouldn't rely on SGOTI for the finest interpretations of tax law.
And I'm pretty sure it's trade dates, not settlement dates, that matter.