Title heading sync broken - Failed to push steps

Please make a clear and concise description of what the bug is.

Steps to reproduce

1. Create new note
2. Set # Heading
3. Save note
4. Click another note
5. See error console

Expected behaviour

No error in console.
Title of Note, on left side is updated with first line of note

Actual behavior

Error in console

Happens in Firefox 139.0.4 and Brave 1.78.102

Errors/Logs

[ERROR] text: Failed to push the steps to the server  Object { app: "text", uid: "xxxxxxxxxx", level: 2, stack: "J@https://my.server.com/apps/text/js/text-editors.js?v=2ed0fdb7-33:2:176176\nNe@https://my.server.com/apps/text/js/text-editors.js?v=2ed0fdb7-33:2:187597\nv@https://my.server.com/apps/text/js/text-editors.js?v=2ed0fdb7-33:2:192273\n", message: "Request failed with status code 403", name: "AxiosError", code: "ERR_BAD_REQUEST", config: {…}, request: XMLHttpRequest, response: {…}, … }
[ERROR] text: failed to write to document - not allowed Object { app: "text", uid: "xxxxxxxxxx", level: 2 }
[ERROR] text: Unexpected Error "Failed to apply steps. Retry!" Object { app: "text", uid: "xxxxxxxxxx", level: 2, error: Error }

Server

Notes app version: 4.12.1
Nextcloud version: 29.0.16, 30.0.11, 31.0.2
OS: Ubuntu 22.04
Web server (from outside to nextcloud): Apache 2.4.x
PHP version: PHP 8.1.x
Database: 10.6.x

Nextcloud configuration:

Workaround

Downgrading Notes to 4.11.0 solves the problem, only in 29.0.16

Reproduce the issue using the listed steps with Notes 4.12.1 and inspect the browser console and failed request associated with text-editors.js. Investigate the 403 response and compare behavior with Notes 4.11.0. Done means saving a heading produces no console error, the steps are accepted by the server, and the note title updates to its first line.