:--)
Writing Nix expressions for Qt libraries and applications is largely similar as for other C++ software. [...]
The major caveat with Qt applications is that Qt uses a plugin system to load additional modules at runtime. In Nixpkgs, we wrap Qt applications to inject environment variables telling Qt where to discover the required plugins and QML modules.
This effectively makes the runtime dependencies pure and explicit at build-time, at the cost of introducing an extra indirection.
-- Taken from Nixpkgs Reference Manual section on Qt
For this reason the quickshell desktop components are run via a wrapped quickshell binary so that quickshell has access to QML components like IdleInhibitor.