What finally seems to have done it is to insert an additional step between 2 and 3 in this sequence: <a rel="nofollow" target="_blank" href="
https://ttlc.intuit.com/questions/1901210-remove-uninstall-turbotax-for-mac">https://ttlc.intuit.com...>
The step "2a" is to Restart the Mac.
Once I did that and again downloaded the 220.5 Mb update. When the download was finished and I pressed the Install and Relaunch button, TTD2018 actually did Relaunch. (Before, it would not relaunch.) TT checked for updates, and for the first time, said there were none and the application was up to date.
