[QUOTE=ownedbycats;4095378](cue JSWolf coming in and saying 'you should use a newer version!!!!')
Not possible - I did say I was running it on High Sierra 10.13.6. 3.48 is the latest version I can run without upgrading to Mojave or Catalina. At one point I did try Mojave, but so much broke on my set-up I reverted to High Sierra.
Running in Debug:
Maddys-MacBook-Pro:~ Maddz$ /Applications/calibre.app/Contents/MacOS/calibre-debug -g
calibre 3.48 embedded-python: True is64bit: True
Darwin-17.7.0-x86_64-i386-64bit Darwin ('64bit', ')
('Darwin', '17.7.0', 'Darwin Kernel Version 17.7.0: Fri Oct 30 13:34:27 PDT 2020; root:xnu-4570.71.82.8~1/RELEASE_X86_64')
Python 2.7.15
OSX: ('10.13.6', (', ', '), 'x86_64')
Interface language: en_GB
Successfully initialized third party plugins: Gather KFX-ZIP (from KFX Input) (1, 36, 0) && DeDRM (6, 8, 0) && Package KFX (from KFX Input) (1, 36, 0) && Set KFX metadata (from KFX Output) (1, 49, 0) && KFX Output (1, 49, 0) && Extract ISBN (1, 5, 0) && View Manager (1, 6, 0) && EpubSplit (3, 0, 0) && Count Pages (1, 11, 0) && Kobo Books (1, 8, 0) && Kindle hi-res covers (0, 5, 0) && Kindle Collections (1, 7, 29) && EpubMerge (2, 11, 0) && Amazon.com Multiple Countries (1, 0, 0) && KFX metadata reader (from KFX Input) (1, 36, 0) && KFX Input (1, 36, 0) && KoboTouchExtended (3, 4, 4) && Kobo Utilities (2, 12, 3)
devicePixelRatio: 2.0
logicalDpi: 72.0 x 72.0
physicalDpi: 113.500001705 x 113.500001705
Using calibre Qt style: True
[0.00] Starting up...
[0.02] Showing splash screen...
[0.19] splash screen shown
[0.20] Initializing db...
[14.41] db initialized
[14.41] Constructing main UI...
DEBUG: 0.0 KoboUtilites::action.py - loading translations
DEBUG: 0.0 KoboUtilites::dialogs.py - loading translations
DEBUG: 0.0 KoboUtilites::action.py - loading translations
[16.54] main UI initialized...
[16.54] Hiding splash screen
[17.56] splash screen hidden
Maddys-MacBook-Pro:~ Maddz$
Opening with no plug-ins worked first time; opening in debug still dropped me out...