I wasn’t able to delete this line: define(‘DB_CHARSET’, ‘utf8’); without affecting my new posts after the upgrade. I have also converted my database from latin1 to utf8 in the meantime, but it didn’t help the old posts.
I finally downloaded the Search and Replace plugin https://www.ads-software.com/extend/plugins/search-and-replace/
Once activated, I was able to “replace” odd characters like ? and a€ by leaving the “with” box blank in the case of double spaces after a full stop (I learned how to type old school and can’t break the habit) or by inserting the correct symbol (ie. & % or whatever character was being replaced by the weird characters) and clicking the “go” button.
Worked like a charm.
This chart helped find some of those codes https://www.web-source.net/symbols.htm