In my monorepo I use multiple resolves, mostly because apps are deployed to different environments and use different sources. How should I go with using one virtualenv for working in IDE (vscode)? Would I need to generate single requirements.txt file with all dependencies and then use virtualenv/pipenv/pdm or some other virtualenv or there is nicer way to do it?

We deploy multiple applications but use one set of requirements across all the apps. With that said, I would imagine that you don't want to create too much divergence between your prod and development environments. If you're using vscode https://code.visualstudio.com/docs/editor/workspaces is a nice solution for specifying multiple roots that can each point to a different venv.