Why does the paragraph button not work in the TinyMCE (Wordpress) editor?

Question

TinyMCE

Why does nothing happen when I click on the Paragraph button in the header of the standard wordpress editor?
Killed 4 hours of time, and could not understand why it does not work.
I checked that it does not work - in text mode. Checked on 2 sites. Gutenberg disabled by hand and plugin.
Headings are inserted.
WP 5.0.3.
functions.php:

add_filter( 'tiny_mce_before_init', 'my_format_TinyMCE' );
function my_format_TinyMCE( $in ) {
    $in['extended_valid_elements'] = 'p[*]';
  return $in;
}

Answer 1

It turns out that it is not visible in a text editor when writing an article, but after publication, the paragraphs miraculously become escaped<p><p>