We just released Mastodon 4.5.5, 4.4.12, and 4.3.18.
These versions contain various bug fixes, including very important (1 high severity, 3 moderate severity) security fixes.
Mastodon 4.2 is now unsupported, so if you still run it, please update to a supported version as soon as you can.
Full release notes and update instructions are available on the GitHub releases page.