In your poetry config, it’s important to indicate that the rasa pro package is pulled from the artifact repository:
...
[tool.poetry.dependencies]
python = ">=3.8.1,<3.11"
rasa-pro = { version = "3.9.4", source = "rasa-pro-python" }
[[tool.poetry.source]]
name = "rasa-pro-python"
url = "https://europe-west3-python.pkg.dev/rasa-releases/rasa-pro-python/simple"
priority = "supplemental"
...