We've had 2 releases in 2 days recently in the Craft 2 line. The latest, 2.922 includes new CP template hooks. There are updates to the updating mechanism itself which means this 2.922 release requires a manual update. There is no one-click-update for this version.
You'll need to download the latest build, dig out
app folder and then replace the
app directory in your site.
One last tip, if you're seeing a Garnish error, just clear your browser cache and Craft's cache and then reload your site. (Some people have manually delete the stuff in
craft/storage/runtime/compiled_templates to get things squared away.)
This documentation page for Craft 3 will probably evolve as we get closer to an actual Craft 3 release, but check out the mention of Craft 4 at the very end of the page. Yes, I said Craft 4.
"The following things have been deprecated, which means that they still work for now, but you will need to change them before upgrading to Craft 4, at which point the backwards compatibility code will be removed completely."