fixed it!
So i had the same issue, what i did to solve it, is what follows:
Went into Macintosh HD ▸ System ▸ Library ▸ Frameworks ▸ NotificationCenter.framework ▸ PlugIns
here you can find the widgets you have installed in you mac, what I did was change the name of weather into com.apple.ncpluggin.Weather.appex ; and stocks into com.apple.ncpluggin.Stocks.appex , I'm not sure if this was necessary, though.
Then I just double clicked in each one, it will open with widget simulator app, press the green button and voila, they now appear in my notification center.
Hope this helped you guys i just created my acc to answer this post as i was reading it since it was created because I had the same problem
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