Within the context menu that pops up whenever you click a block, The context menu showing “Clone - Edit - Delete - Cancel”, it should have (Backspace) underneath “Delete” to show you can press this instead of manually deleting things. Not that I’ve ever read the user guide at https://flowlab.io/user_guide/, but even this doesn’t seem to mention “backspace” at all after searching it with CTRL-F. Would probably help some people out.
I’ve been manually click-deleting every single block until just now. I did try the delete key at first, that was the only obvious one i thought block deletion would be I suppose, but today I must have hit backspace on accident leading me to finally ‘discover’ this shortcut.