Some on this board may think that governments are incapable of keeping something like UFOs secret for long periods of time.

You need to go no further than the Ultra Secret. The UK, later the U.S. and other Allies were given access to enemy encrypted messages in WWII. This remained secret through the War and largely secret for almost thirty years until F. W. Winterbotham, CBE published his book The Ultra Secret. When I first learned of this publication I could not believe it until I read his book for myself.

For the impact of Winterbotham's book see THE HISTORICAL IMPACT OF REVEALING THE ULTRA SECRET by DR. HAROLD C. DEUTSCH 1977:
https://apps.dtic.mil/sti/tr/pdf/ADA512192.pdf

Also see:
https://en.wikipedia.org/wiki/F._W._Winterbotham

The truth has been hiding in plain site......for years.

Admiral Roscoe Hillenkoetter:
1st Director of the CIA (1947-1950)
"It is time for the truth to be brought out....Behind the scenes, high-ranking Air Force officials are soberly concerned about UFOs. But through official secrecy and ridicule, many citizens are led to believe the unknown flying objects are nonsense....I urge immediate Congressional action to reduce the dangers from secrecy about Unidentified Flying Objects."
Hillenkoetter, Roscoe; "Aliens from Space", Major Donald E. Keyhoe, 1975

(Please note the "dangers" that Hillenkoetter talks about are from SECRECY not from the UFOs.