Default templates not working - blank.ott and blank.dotx

Describe the bug
Can't overwrite Blank template in Settings > Office > Global Templates, nor appdata_[instanceid]/richdocuments/empty_templates/

I tried adding a Blank.ott in Settings > Office > Global Templates which appears as a template but does not overwrite the default. "Blank" still appears, as well as our desired "Blank":

After searching, I found the Collabora documentation which states to replace document.ott with our desired template in appdata_[instanceid]/richdocuments/empty_templates/ but that didn’t work either unfortunately. The Blank template does not overwrite the default.

We are using Collabora Online - Built-in CODE Server version 22.5.401 and Nextcloud Office 6.1.1 on Nextcloud 24.0.3.

We are also using this setting ticked in Settings > Office > Advanced Settings to use Open XML and hence DOTX template, but I also tried OTT file and that didn't work either.

Expected behavior
To be able to replace Blank template in Settings > Office > Global Templates

Server details

Operating system:
Ubuntu 20.04.4 LTS

Web server:
nginx/1.18.0

Database:
psql (PostgreSQL) 12.11

PHP version:
PHP 8.0.14 (cli) (built: Dec 20 2021 21:22:38)

Nextcloud version:
24.0.3

Version of the richdocuments app
Nextcloud Office 6.2.0

Version of Collabora Online
Collabora Online - Built-in CODE Server 22.5.502

{"reqId":"vqtPs3nOafJSNdaJEhZk","level":3,"time":"2022-08-11T08:15:02+10:00","remoteAddr":"","user":"--","app":"integration_whiteboard","method":"","url":"--","message":"[ERROR] Spacedeck is unreachable, it might not be running. cURL error 7: Failed to connect to localhost port 9666: Connection refused (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for http://localhost:9666/api/spaces","userAgent":"--","version":"24.0.3.2","data":{"app":"integration_whiteboard"},"id":"62f43b11ef294"}

Reproduce the issue through Settings > Office > Global Templates using both Blank.ott and the Open XML/DOTX setting, then compare that behavior with appdata_[instanceid]/richdocuments/empty_templates/ and the linked Collabora template documentation. Done means the custom Blank template replaces the default Blank entry in both relevant configurations.