Both Pakistan and South Africa were invited yet declined to participate. Both countries appear on the State Department's participant list, yet on December 8th, Pakistan's Ministry of Foreign Affairs released the below statement:
We are thankful to the United States for inviting Pakistan for
participation in the Summit for Democracy, being held virtually on
9-10 December 2021.
Pakistan is a large functional democracy with an independent
judiciary, vibrant civil society, and a free media. We remain deeply
committed to further deepening democracy, fighting corruption, and
protecting and promoting human rights of all citizens. In recent
years, Pakistan has instituted wide-ranging reforms aimed at advancing
these goals. These reforms have yielded positive results.
We value our partnership with the U.S. which we wish to expand both
bilaterally as well as in terms of regional and international
cooperation. We remain in contact with the U.S. on a range of issues
and believe that we can engage on this subject at an opportune time in
Pakistan will, meanwhile, continue to support all efforts aimed
towards strengthening dialogue, constructive engagement, and
international cooperation for the advancement of our shared goals.
I don't think South Africa has released an official statement on President Ramaphosa's non-attendance, however the Daily Maverick has carried statements from his acting spokesman, Tyrone Seale, as well as International Relations and Cooperation Minister, Naledi Pandor:
The president’s acting spokesperson, Tyrone Seale, offered the West
African visit as a reason for the Ramaphosa not attending Biden’s
“We are just wrapping up our West Africa visit today. We will not be
summiting,” he told Daily Maverick.
International Relations and Cooperation Minister Naledi Pandor hinted
at another reason for declining the invitation, in an interview with
Daily Maverick journalist Carien du Plessis last Saturday in Accra,
Pandor said she had received the invitation letter the day before and
that she was taken aback.
“The letter says things like, ‘America, a country that has always
supported human rights.’ Really?”
Pandor suggested that perhaps her government declined the invitation
because it thought a US summit for democracy lacked credibility.