I would like to know if there is a way to create output data sets directly through a R notebook
You will not be able to create the dataset through the R API. However, just like a recipe does, you can write the content of any existing dataset.
share the R notebook with other colleagues
You can provide notebook templates, typically you would do this through a plugin, here is the documentation about this component. https://doc.dataiku.com/dss/latest/notebooks/predefined-notebooks.html#creating-your-own-prebuilt-templates
Also, can a R notebook be created and executed independently without an R recipe in the DSS project/flow
When creating an R recipe, you can convert it to a notebook, and vice versa. You cannot have a notebook as a step in the flow. You can run a notebook and do whatever you want, but this will not appear in the flow, so it's not great for reproducibility and auditing.