Sumana

I thought "how do I know this for sure?" once you asked. I remembered having heard for years that former presidents were entitled to continuing intelligence briefings if they wanted them. I double-checked just now and I believe I am mostly right; the specific thing that ex-presidents can get may not specifically be the PDB but it's much more detailed and classified-y than what regular folks like me can see. I pulled up some citations:

Michael Morell, who led the CIA during the Benghazi assault and had previously served as Bush's PDB briefer, described the PDB process at length in his book, "The Great War of Our Time."

Morell wrote that he began compiling intelligence at around 4 a.m. every day — organizing, synthesizing and ordering them to present to the president and his inner circle, which he said almost always included Vice President Dick Cheney, then-national security adviser Condoleezza Rice and chief of staff Andy Card. Occasionally, Bush’s father, former President George H.W. Bush, would join the briefings, a right generally afforded to former presidents.

Cheney, Kyle. "Benghazi Probe Offers a Road Map for Trump’s Russian Bounty Briefing." Politico, Jul 02, 2020.

President Trump on Tuesday denied a report that he had considered restricting former president Barack Obama's access to intelligence briefings, calling that an extraordinary step that he "never discussed or thought of."

The New Yorker reported Monday that then-national security adviser H.R. McMaster had talked Trump out of the idea, which some White House officials were pushing last year in the wake of Trump's assertion, without evidence, that Obama had ordered wiretapping of Trump Tower during the 2016 election campaign.

Living former presidents have access to intelligence briefings, in part because they often continue to meet with foreign leaders and represent the United States.

Wagner, John. "Trump Denies Report that He Considered Restricting Obama’s Intelligence Briefings." Washington Post, Aug 21, 2018.