bytesmiths

<palmforehead>I should have thought of that!</palmforehead>
 
Thank you thank you thank you! That did it.
 
One thing a little weird… Alfred had the right boxes ticked, so I tried cycling them, and the Alfred box in Accessibility would not un-tick. So rather than go into Terminal as your second link suggests, I used the "minus" box to remove Alfred entirely from the Accessibility list, then used the "plus" box to re-add it, then it would toggle ticks as it should. Then all was good!
 
Sorry to have bothered you. I did go through the FAQs and such, searching for "Snippet", but didn't find that suggestion to examine System Preference needs.
 
Take it as a testament to your normally smooth upgrades that I've become spoiled!

@bytesmiths Normally, when a user isn't able to expand snippets or paste from clipboard but the features appear enabled in Alfred's preferences, it's because of broken Accessibility permissions.
 
You'll need to grant permissions here:
https://www.alfredapp.com/help/getting-started/permissions/#integration
 
If they already appear to have been previously granted, follow the steps to clear and re-grant them, as these most likely became corrupted during your upgrade:
https://www.alfredapp.com/help/getting-started/permissions/#regrant
 
This comes with the caveat that you're updating / maintaining your Mac in non-standard ways, so it's possible that your issues with permissions are coming from this.