How do I find out more information about a pending software update?
From the provided result, the Security update "061-90745" is an update still trying to be installed for Mojave! 



Clear the old update with defaults delete com.apple.preferences.softwareupdate LatestMajorOSSeenByUserBundleIdentifier &amp;&amp; softwareupdate --list

It removes the old incompatible string then refreshes the list from Apple

Congrats on the move to Catalina!