Apple's own update page now lists macOS 27 Golden Gate at the top of its compatibility table, alongside Tahoe 26 and the older releases still in use. Apple has also been shipping security fixes for older versions, like the critical Neural Engine bug patched in Sequoia 15.7.8 and Tahoe 26.6. Whichever macOS your Mac runs, the first job is the same: make sure it's up to date.

Photo: KKPCW（Kyu3） / Wikimedia Commons (CC BY-SA 4.0), cropped