Uncommon, but achieved seven times by five players in 25 years between 1974 and 1998 (end of Sampras peak):
Connors '74
Wilander '88
And in era when Australian not treated as a Major:
Borg '79 and '80 (RG, Wim., YEC)
McEnroe '84 (Wim, USO, YEC)
Lendl '86 and '87 (RG, USO, YEC)
As someone mentioned, Pete held three titles simultaneously in early 1994. But nobody was going to win 3 out of 4 calendar year in the Sampras era because Sampras was the best player hands-down 1993-97 and he was not going to achieve it. Interesting is 1997, Pete's last peak year. Australian, Wimbledon, then finish year with blitz through Paris, YEC and GSC. And 1994 is AO, Sunshine Double, Italian Open, Wimbledon and YEC, among a total 10 titles for the year. Great seasons but not 3 of 4 Slams.
In 25 seasons 1999-2023, achieved eight times by three players: Fed '04, '06, '07; Rafa '10; Novak '11, '15, '21, '23.
Post-War Amateurs, five times in 22 seasons: Trabert '55, Hoad '56, Cooper '58, Laver '62, Emerson '64.
Post-War Pros four times by three players in 22 seasons: Gonzalez '56, '57, Rosewall '63 (4 of 4), Laver '67 (4 of 4)
Early Open Era: Laver '69