IWAs haven't launched for unmanaged devices, though ChromeOS-only unmanaged support is on the roadmap for 2025 (unmanaged WML support isn't in the short-to-medium term plans).
Dev mode is currently required because we haven't enabled a way to mark signing keys as trusted, but that's coming in a limited form with the ChromeOS unmanaged launch.
For a more user friendly installation experience you can try enabling these flags:
- chrome://flags/#enable-isolated-web-app-dev-mode
- chrome://flags/#enable-isolated-web-app-unmanaged-install
Then double click on a .swbn file from the ChromeOS Files app, which should launch an installation UI. Note that the UI is still missing some polish, but should work. It currently installs the IWA as dev mode, but will eventually install as non-dev unmanaged.