This is very similar to ✨ The drupal/section block should use configurable element Needs work , with the same reasons:
When using the drupal/section block provided by this module the resulting output contains the HTML element. There should only ever be one of these as it is a landmark role in ARIA and at the same level as other landmarks
Most Drupal themes + core includes a <main> section further up in the DOM, which I'd argue in the vast majority of cases would be more correct. Also, <main> can not be below <article>, which is a thing that can typically happen here, and will cause validation errors.
In comparison with the issue above, I think it is overly complex to make this configurable. That would also create a need to have a UI to configure it on the block instance.
I suggest one of two alternative directions:
main element in, so people can change it to their liking using a template override.Active
3.0
User interface
Here's a PR adding a template file with the main tag, not breaking any markup, but adding flexibility to override it in your custom theme.
In a future major version (4?) I'd still suggest changing the template file to use a div, as this will be correct in most cases.