Yeah, it was caused by updating to macOS 11, sadly. Apple has yet to make it possible to use tabs with the type of window that Scapple uses (the new “borderless” look). Hopefully they fix this in a future update.
I’ve just updated to Big Sur and I’ve found this problem. It’s a huge one, because when one works with lots of documents, not being able to open them in tabs makes the work confusing and hard.
Aren’t the developers planning to fix this instead on relying on an update from Apple? The previous message was from two months ago and still there’s no Big Sur fix for this.
Please, we need Scapple to be kept alive and fixed when it needs to.