In short, add

layout python3

to .envrc.

To customize the name the virtualenv, prepend export VIRTUAL_ENV=your_venv_name.

• https://github.com/direnv/direnv/wiki/Python - official docs
• https://github.com/direnv/direnv/issues/1264 - Activate python venv by default?
• https://github-wiki-see.page/m/direnv/direnv/wiki/Python
• https://stackabuse.com/managing-python-environments-with-direnv-and-pyenv
• https://www.keiruaprod.fr/blog/2023/01/26/using-direnv.html

And also, completely new to me, it is possible to use direnv with Github Actions (with a complete example in the direnv docs).