Culture, Arts, Libraries, and Museums Emergency Relief Act of 2020 or the CALMER Act of 2020 This bill appropriates additional amounts for (1) the National Endowment For the Arts, (2) the National Endowment for the Humanities, and (3) the Institute of Museum and Library Services. Specifically, the funds shall be used to expand digital network access, to purchase tablets and other internet-enabled devices, to provide technical support services, to assist museums with operational expenses, to develop and share distance learning content, and for pandemic recovery planning and implementation. The bill (1) eliminates the $300 limitation on the tax deduction for the charitable contributions of nonitemizing taxpayers and extends such deduction through 2021, (2) extends the modification of the limitation on the tax deduction for charitable contributions through 2021, (3) exempts tax-exempt charitable organizations from payment of employment taxes in 2020, (4) extends eligibility for the Main Street Lending Program to tax-exempt organizations, and (5) extends eligibility for the Paycheck Protection Program to all tax-exempt charitable organizations.