As @ipa-mdl said, it seems to be caused by installing without using the signed-by option.
I didn’t realize that. Thank you for letting me know, @ipa-mdl!
The environment was set up in 2020 and apt upgraded since then, so that’s probably the cause.
How about guiding ROS 2 users who set up before April 2021 to use “apt-key add”, which is the same approach as ROS1?
This is the result of sudo apt -oDebug::pkgAcquire::Worker=1 update 2>&1 | tee log.txt.