Thanks for your reply, it’s extremely informative and useful. It’s actually the second time I’ve resized the APFS container and this didn’t happen the first time. I was also shocked to wake up this morning to discover the resize had actually left me with a new partition, considering that every time I tried to resize it, the process failed with a well documented error code or the machine just spontaneous rebooted while frozen.
One other question I have is, that once I’d installed Fedora, my Mac would automatically boot into Fedora. So now if I want to use macOS I have to use the Option key. Has the Fedora boot loader over written something and is it even possible to swap it back? I’m going to give the net installer Rescue a bash now. Thanks.