This security and maintenance release features 23 fixes and enhancements. Plus, it adds a number of security fixes—see the list below.
These bugs affect WordPress versions 5.4.1 and earlier; version 5.4.2 fixes them, so you’ll want to upgrade.
If you haven’t yet updated to 5.4, there are also updated versions of 5.3 and earlier that fix the bugs for you.
Read the detail here: https://wordpress.org/news/2020/06/wordpress-5-4-2-security-and-maintenance-release/