: Since version 3.28 is a past release, you can find installers for Windows, macOS, and Linux in the QGIS hosted downloads repository macOS Specific : Older macOS installers are specifically cataloged in the QGIS macOS archive Release Announcement
To download QGIS 3.28, you can visit the official QGIS website: qgis 328 link download
28 specifically to maintain with a certain plugin or tutorial ? Download - QGIS : Since version 3
: Follow the official installation instructions for your specific distribution (Ubuntu, Fedora, Debian, etc.). Why use QGIS 3.28? you can find installers for Windows
: For security, you can verify the SHA256 sum provided on the download page to ensure your installer hasn't been tampered with.
Essential plugins are more likely to be fully functional.