[KevinH]

Also since we run the EmbeddedPython routines explicitly without env vars, we are going to have to change python3lib updatechecker.py to set its own environment var for macOS just to be safe.

Edit:
So something like this added to our updatechecker.py inside Sigil's python3lib or added to any plugin should do the trick too.

import sys
import os

if sys.platform.startswith('darwin'):
    try:
	    import certifi
	    os.environ["SSL_CERT_FILE"]=certifi.where()
    except:
	    pass

Update:

With both changes to updatechecker.py for our python3lib and to PluginRunner.cpp, and after I removed the bad symlink changes done by the install certify script, I was able with a clean rebuild to run EpubCheck and its update checker found a new update and downloaded it and ran.

So I pushed all of these changes to master. In the interim, if a plugin wants to do an update check prehaps they could add the short macOS piece of python code near the top to get the current release to work.