Challenges getting first Outlook Web Add-in to run

Question

I am trying to get my first Outlook Web add-in to work. So I:

• Followed the instructions at https://learn.microsoft.com/en-us/office/dev/add-ins/tutorials/outlook-tutorial "Tutorial: Build a message compose Outlook add-in"
• Per those instructions, I used the Yeoman generator to create an Office Add-in Task Pane project for Outlook. I followed the instructions to the "Test the generated add-in". So only the manifest had been changed. A very simple add-in at this point.
• Tried npm start from the command line. npm start office-addin-taskpane-js@0.0.1 start C:\Users\Lindsay\OutlookTestAddin2\OutlookTestAddin2
  office-addin-debugging start manifest.xml Debugging is being started...
  App type: desktop
  Enabled debugging for add-in a35130ed-92ee-4a47-a5e2-4588da510b2e.
  Starting the dev server... (webpack serve --mode development)
  The dev server is running on port 3000. Process id: 14044
  Sideloading the Office Add-in...
  Debugging started.
• At this point, I can view the welcome page in a browser at the URL https://localhost:3000/taskpane.html.
• Outlook is started with as a result of npm start. There is no "Show Taskpane" button to be found anywhere in Access.
• Navigated to https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/sideload-outlook-add-ins-for-testing to follow instructions for "Sideload manually". This PC has Outlook 2016, so went to that section.
• It says to select the "Get Add-ins" button, but this button is greyed out.
• Checked File > Options > Trust Center > Trust Center Settings > Privacy Options > Privacy Settings and looked for “Enable optional connected experiences” as noted in http://makerblock.com/2021/05/how-to-fix-outlook-get-add-ins-grayed-out-button/ and several other pages. “Enable optional connected experiences” does not exist in my Outlook installation. "Turn on all connected experiences" does exist and is enabled.
• Looked at other alternatives for sideloading problems. Found https://stackoverflow.com/questions/58436093/unable-to-sideload-outlook-add-in says "It turns that under settings you may need to turn on which "actions" are available in your read/compose pane." I am not finding exactly to which "settings" this refers.
• Tried the same on a different PC with Office The results were essentially the same: No "Show Taskpane" button and the "Get Add-ins" button is greyed out. In this case, “Enable optional connected experiences” exists and is checked.

What am I missing here?
Thanks in advance...