Disallow HTML in comments I'd like to disallow all HTML and only allow plain text in comments across the site for all users, authenticated or not, but I still want to use other HTML filters for other content types. How can I achieve that in Drupal 8?

I've created a custom text format called "No HTML" and set it as the default format for comment bodies at admin/structure/comment/manage/comment/fields/comment.comment.comment_body. But instead of disallowing all HTML, it gives the option to change the text format to any other format available to the user.

How can I get comments to only use my "No HTML" text format for all users without disabling the other text formats for other content types?
The Allowed Formats projects allows you to control the available text formats per field, so you can limit it to plain text. Better Formats is a similar module.

You could do the same with a form alter and set #allowed_formats on the form element. Or you could remove the default comment body field and replace it with a plain text field. Although there might be some code relying on the name/existence of the default body field.