PyWebView with CEF: CEF window with UID master does not exist

Question

i want to open a WebApp using Webview/CEF. Im using Python3.9.18 since i need CEF.

When i run the sample minimal example:

        import webview
        from cefpython3 import cefpython as cef

        webview.create_window('test', 'http://www.stackoverflow.com')
        webview.start(gui='cef')

it tells me: "CEF window with uid master does not exist"

but at least opens the window.

If i create an .exe with pyinstaller and run it, it doesnt open the window and tells me "Invalid file descriptor to ICU data received"

Versions: WebView 4.4.1 Pyinstaller 6.3.0

Im quiete new to this and dont know what to do with these error messages. Tried those tipps to the best of my abilities, but still the same: https://github.com/pyinstaller/pyinstaller/issues/5400

Any help would be greatly appreciated