the App Store says there are no updates to os even though it has an old ver

A 2018 modelcan be upgraded to the current version of Monterey macOS 12. See: How to upgrade to macOS Monterey - Apple Support

or if you want an earlier version, see: How to get old versions of macOS - Apple Support

Safari is update when you upgrade the OS on your Mac. If you reply with your Mac model (e.g., iMac, MacBook Air, etc) and model year someone here can provide more information. Both of those are available at Apple menu > About this Mac.