https://www.macworld.co.uk/news/mac-software/problems-macos-catalina-10154-3785841/MacOS Catalina 10.15.4 was released a few weeks ago - but don't rush to install the update just yet, because multiple users say it creates more problems than it fixes.
Some have found that the hard drive in an updated machine continually spins even when the Mac is supposed to be asleep, which could cause damage; others report system crashes when waking from sleep (involving a kernel panic and reboot to the Apple logo), and problems when copying more than 30GB of data.
Hopefully the bugs are fixed in macOS Catalina 10.15.5, which is currently being beta tested. Affected users can of course also try downgrading to an older version.
MacRumors has asked Apple for a comment, but at time of writing, had received no response. However, the company has pushed out an additional update that does not raise the version number. It is not clear if this update solves the major issues outlined in this article.