From Breitbart:

According to the FBI, there were 2,911,128 background checks conducted in April 2020. The closest any other April came to that figure was in 2019, when 2,334, 294 NICS checks were done.
April’s surge in background checks followed a March that shattered all one-month records. Breitbart News reported March 2020 witnessed 3,740,688 background checks, which were the most checks conducted in any single month since the inception of NICS.