Removing those files from upgrade_changes.txt did the trick. The upgrade script continued on its way.
I then encountered this problem
with image libraries. Using Ruben's advice there, I updated each image setting in the Control Panel / Styles section. Running happy as a clam on PHP 7.3.
I still have to update the forum view settings for non-admin users. Then it's off to push from my test machine to the live site.
Thanks all again for the help!
jjjjj, I hope you have similar success and I apologize for taking this thread over.