Every time I quit or restart anki, this message pops up - so I can't use it

An error occurred. Please start Anki while holding down the shift key, which will temporarily disable the add-ons you have installed.
If the issue only occurs when add-ons are enabled, please use the Tools>Add-ons menu item to disable some add-ons and restart Anki, repeat until you discover the add-on that is causing the problem.
When you’ve discovered the add-on that is causing the problem, please report the issue on the add-ons section of our support site.
Debug info:
Anki 2.1.44 (b2b3275f) Python 3.8.6 Qt 5.14.2 PyQt 5.14.2
Platform: Mac 10.16
Flags: frz=True ao=True sv=2
Add-ons, last update check: 2021-07-21 22:04:43

Caught exception:
Traceback (most recent call last):
File “aqt/taskman.py”, line 88, in _on_closures_pending
File “aqt/taskman.py”, line 59, in
File “aqt/taskman.py”, line 77, in wrapped_done
File “aqt/sync.py”, line 114, in on_future_done
File “aqt/main.py”, line 914, in on_collection_sync_finished
File “aqt/main.py”, line 691, in reset
File “aqt/main.py”, line 653, in moveToState
File “aqt/main.py”, line 675, in _reviewState
File “aqt/reviewer.py”, line 69, in show
File “aqt/main.py”, line 992, in setStateShortcuts
File “aqt/main.py”, line 983, in applyShortcuts
TypeError: argument 1 has unexpected type ‘NoneType’

Please use shift as directed in the message above.