Can you choose which folders use real-time push vs which folders use polling?
I’m afraid not. I’m pretty sure the entire account uses polling. I’ll usually open the app and hit F5 to quickly poll for results, otherwise I’m waiting for the next sync.
Having said that, the unread counter works fine for sub-folders:
Edit: I was wrong, Mailspring uses the IMAP IDLE extension to wait for new mail delivery. Still doesn’t stop me from spamming F5 when I’m waiting for new mail to arrive.
dan