Autostart KCM does make copy of desktop file if derived from Application. This basically works. But as soon as Application launchers are edited via KDE Menu Edit their properties are out of sync. So maybe a symbolic link to the source desktop file is better?
Thank you for the bug report! However Plasma 6.2.1 is no longer eligible for support or maintenance from KDE; supported versions are 5.27. (LTS), and 6.3 (non-LTS) or newer. Please upgrade to a supported version as soon as your distribution makes it available to you. Plasma is a fast-moving project, and bugs in one version are often fixed in the next one. If you need support for Plasma 6.2.1, please contact your distribution, who bears the responsibility of providing support for older releases that are no longer supported by KDE. If you can reproduce the issue after upgrading to a supported version, feel free to re-open this bug report.
A simple symlink might indeed make more sense until we have a better method of reference/inheritance here.