Hey!! I can help.
So D2R is Cross-Progression, meaning your online characters and stash are saved to your Battle.net account, allowing you to switch between PC and consoles seamlessly. You would need to purchase the game on both platforms in order to access each one. Now, it is not Cross-play, meaning you will not be able to see/play with anyone from the different platform while playing.
You do have an advantage of being able to trade/post in both forums, as you will have access to conduct either trade by switching to the correct platform.
adding to this, while playing on the Nintendo Switch, You can ONLY play up to 4 Players Max, here is a video I found helpful which goes over comparisons and Pros & Cons of the Switch.