In 2016 Apple introduced the possibility to install a beta on the Mac alongside the final version of Safari. Now a new version of the Safari Technology Preview has been released again. The release bears the number 139 and, as usual, is intended to give users a foretaste of the coming changes in the browser.
The update is available via the software update function in the system settings. If you haven’t installed the preview yet but would like to try it out, you can get the version for Big Sur or Monterey from the Apple Developer website. As already mentioned, parallel use with the final version of Safari is possible.