Toggle heading with content is saved as a regular heading and paragraph

Have XWiki Jetty/HSQLDB 18.5.0 with the experimental BlockNote editor installed. Configure BlockNote as the default editor.

Steps to reproduce

1. Create or edit any wiki page.
2. In editor, insert a Toggle Heading block any level.
3. Name such heading and provide the toggle content.
4. Save the page.

Actual result

The toggle heading is converted into a regular heading, and the toggle content is converted into a normal paragraph. The collapsible behavior is lost.

Expected result

The toggle heading is preserved as an interactive collapsible heading. The toggle content is hidden by default and revealed when clicking the toggle, as in the BlockNote demo .