A headline cannot be "downgraded" to normal text

Once a line has been marked "heading" as H1, H2, .. H6 it cannot be made regular text anymore. (Maybe I am too stupid to find it, but then it should be more obvious ;-) )
Nothing seems to help: clicking on the [H1]-button only offers H1..H6, editing the text does not influence the "#" and even copying the text and pasting it somewhere else keeps the headline feature.
Generally it might (additionally) be an option to add an "edit source code button" for the more tricky modifications.

Steps to reproduce

1. Start note, input some text, mark a line as Heading
2. Try to make that line regular text again

Expected behaviour

The [H1]-button should offer an option "regular text" inside its drop-down

Actual behaviour

Text, once marked "Heading" stays so, forever

Server

• Notes app version: 4.2.11
• Nextcloud version: 31.0.6
• OS: debian linux 12 (bookworm)
• Web server: apache2 2.4.62-1~deb12u2
• PHP version: PHP 8.2.28
• Database: mariadb 1:10.11.11-0+deb12u1

Nextcloud configuration:

{
"system": {
"memcache.local": "\OC\Memcache\APCu",
"logdateformat": "F d, Y H:i:s",
"passwordsalt": "REMOVED SENSITIVE VALUE",
"secret": "REMOVED SENSITIVE VALUE",
"trusted_domains": [
.... various ....
],
"datadirectory": "REMOVED SENSITIVE VALUE",
"dbtype": "mysql",
"version": "31.0.6.2",
"overwrite.cli.url": "http://localhost",
"dbname": "REMOVED SENSITIVE VALUE",
"dbhost": "REMOVED SENSITIVE VALUE",
"dbport": "",
"dbtableprefix": "oc_",
"mysql.utf8mb4": true,
"dbuser": "REMOVED SENSITIVE VALUE",
"dbpassword": "REMOVED SENSITIVE VALUE",
"installed": true,
"instanceid": "REMOVED SENSITIVE VALUE",
"maintenance": false,
"theme": "",
"loglevel": 2,
"mail_smtpmode": "smtp",
"mail_sendmailmode": "smtp",
"maintenance_window_start": 1,
"default_phone_region": "DE",
"skeletondirectory": "/home/nextcoud_data/skeleton",
"mail_from_address": "REMOVED SENSITIVE VALUE",
"mail_domain": "REMOVED SENSITIVE VALUE",
"mail_smtphost": "REMOVED SENSITIVE VALUE",
"mail_smtpport": "587",
"mail_smtpauth": 1,
"mail_smtpname": "REMOVED SENSITIVE VALUE",
"mail_smtppassword": "REMOVED SENSITIVE VALUE"
}
}

Client

Please complete the following information.

• Browser (incl. version): firefox 140.0.2 (64-Bit)
• OS: archlinux

Start by reproducing the issue in the Notes editor using the listed steps and inspect the heading dropdown behavior. Done means a heading can be changed back to regular text, with the editor no longer preserving the heading marker after the change.