"Pelosi’s staffers deliberately weakened security at the U.S. Capitol for Jan.6"
False, Pelosi's role as the House Speaker does not direct the National Guard, but she and the Senate Majority leader called for military assistance, including the National Guard. I doubt the staffers weakened security, but Pelosi certainly didn't block the National Guard.
https://apnews.com/article/fact-checking-235651652542
"and ordered a cover-up."
What cover-up?
"Steven A. Sund, the Capitol Police chief on that fateful day, not only confirms her culpability along with the rest of the Democratic leadership,"
There is no evidence that Sund blamed Pelosi and the rest of the Democrat leaders for the Jan 6 insurrection, instead Pelosi called Sund to step down because his request of the National Guard being placed on standby was turned down by House and Senate security officials.
https://www.usatoday.com/story/news/politics/2021/01/11/steven-sund-national-guard-help-capitol-riots/6620195002/
"but also how his own agency and the intelligence community let the Capitol attack happen."
Steven Sund wrote in his new book "Courage Under Fire: Under Siege and Outnumbered 58 to 1 on January 6" that the federal government’s multibillion-dollar security network provided no such shield on Jan. 6. He even alerted the FBI, the department of Homeland Security, and even his own agency's intelligence unit that there could have been an attack on the Capitol. He said those agencies didn't even take the basic steps to assess those plots or sound an alarm.
Yes, you are correct on what the problems with the agencies Sund contacted before the insurrection.
https://www.washingtonpost.com/nation/2023/01/01/steven-sund-capitol-police-book-jan6/
I recommend if you want more information on the Jan 6 insurrection, there is a brand new book which I think it was released today that is called "Courage Under Fire: Under Siege and Outnumbered 58 to 1 on January 6" for about $30 USD from eBay.