I think they are wondering if one extension can use both v2 and v3 APIs at once? As in whether v3 APIs will be “backported” to allow v2 extensions to use them

Regarding your mouse double clicking, some Reddit users suggest pressing the click button quite hard a few times…

re: OneNote

Although not a replacement for OneNote on Windows 10/OneNote in Microsoft 365, you can get Waydroid and run OneNote’s Android app with it.

I don’t have a stylus so I’m not able to check if everything works, but if it does, it’ll hopefully feel better than the web client, which wasn’t able to keep up with stylus strokes last time I checked. The number of pens is lacking though, even the iPadOS version is better…