@cketti, thank you very much for posting the link How do I update an existing Gmail account to use OAuth 2.0?
After months of having to check my Gmail accounts on my computer only, I have finally found the time to implement the directions at the above link for getting my Android devices back into order. It was easy to do so, and now all three of my Android devices are easily retrieving and send email from my Gmail email accounts.
To any other K-9 user out there who has been frustrated by K-9’s seeming inability to retrieve Gmail emails, please know that following the manual directions at the above link is easily done, and that within minutes K-9 can be once again retrieving emails from all over the place (for me K-9 is again retrieving emails for me from Yahoo, Hotmail, and Gmail).
I’m delighted that K-9 is once again the King of Android email apps! 