Short answers, pulled from the story.
Only three recordings featured contributions from all four ex-Beatles: "Free as a Bird" (1995), "Real Love" (1996), and "Now and Then" (2023). All three were released under the Beatles name and incorporated Lennon recordings made before his death.
Ringo Starr's 1973 album Ringo is the only album released during Lennon's lifetime to include compositions and performances by all four ex-Beatles, though they contributed to separate songs rather than recording together simultaneously.
Lennon and McCartney recorded together only once after the break-up, in an unreleased jam session on the 28th of March 1974, later bootlegged as A Toot and a Snore in '74. They never recorded together again after that session.
George Harrison staged the Concert for Bangladesh in New York City in August 1971. Ringo Starr participated in the concert alongside Harrison.
Paul McCartney and Ringo Starr have performed and recorded together on several occasions since Harrison's death in 2001. Their collaborations have continued through the 2010s and 2020s, including on Starr's albums Give More Love (2017), What's My Name (2019), and the forthcoming McCartney album The Boys of Dungeon Lane.
Ringo's Rotogravure (1976) included compositions by all four ex-Beatles, but George Harrison did not play on the album. It came closer to a full four-way collaboration than most post-break-up projects, though it fell short of featuring all four as performers.