Events not usually included with regular posts

I’m building a new site for an artists’ guild. We want to show calendar events along with regular blog posts on the blog archive page on our site. We also plan to use Mailchimp to send a daily email digest that contains all the new events and posts.
Using V5.1.5 of TECalendar with Virtue theme, and have tested with TwentySixteen through TwentyTwenty. Everything is updated.

On archive pages for blog posts, behavior varies:
– the archive page is assigned in WP Settings > Reading > posts_page: No control is provided to select a template, so I don’t know what template is used. Events are shown (click “Blog Test” menu item to see this example)
– the archive page is not the one assigned as the …Reading > posts_page: Using the Blog page template from whatever theme is active to make a page a blog archive. Events are NOT shown. (click “Blog” menu item for this example) This COULD be a template issue.
I have tried several widgets for showing recent posts in a sidebar, and none of them show the events. I can’t explain this as a theme or template issue.
My test with Mailchimp showed that events are included with the blog posts only in the RSS feed from the one WP default archive page (assigned in WP Settings > Reading) that is showing both event posts and blog posts.
Is it expected behavior that events only go to the site’s single dedicated page selected in the Reading settings and with no assignable template, or should the events be included everywhere that blog posts are shown or listed?
It would be helpful to know, at a not-very-technical level, how you are enabling the event posts to get into the main blog loop. Are you giving them the regular PostType, creating a custom PostType and telling WP to include this custom PostType when it collects the regular posts, or some other clever scheme?
Thank you!

The page I need help with: [log in to see the link]