@PLuS Thanks for your feedback , fixed it.

The desktop file created by gendesk uses "mockoon-git" (the pkgname) as exec, but the app is built as "mockoon".

This patch fixed it:

--- PKGBUILD.orig       2025-07-04 09:21:15.308429019 +0200
+++ PKGBUILD    2025-07-04 09:15:23.096218561 +0200
@@ -57,7 +57,7 @@
         --pkgdesc="${pkgdesc}" \
         --categories="Development" \
         --name="${pkgname%-git}" \
-        --exec="${pkgname} %U"
+        --exec="${pkgname%-git} %U"
     export ELECTRON_SKIP_BINARY_DOWNLOAD=1
     export SYSTEM_ELECTRON_VERSION="$(electron${_electronversion} -v | sed 's/v//g')"
     HOME="${srcdir}/.electron-gyp"