This is by far one of my favorite Sync for Reddit (and now Lemmy) features.

Do you want to go to a different subject from your current feed but you don't want to lose the feed position? Just hold the community or post you want to go and it will open into another "app window"

Sync for Reddit/Lemmy already handles the RAM in a glorious way by not being closed or losing the content that quickly like many other apps, with this nice extra handy feature you can even improve more your navigation!

EDIT: The feature is called "Long press cards to open comments in the background" and you can check it here:

Settings shortcut: Post options > Long press cards to open comments in the background

It only works in cards and slide views for posts, and I think it works for communities in the explore section with any view type.