Do you have a suggestion for a certain dark theme?
The Qvip Design ones don't seem like they include mandatory branding, here are the two that caught my eye:
https://pluginstore.woltlab.com/file/6564-rayoff-5-2/
https://pluginstore.woltlab.com/file/6001-black-swan-5-2/
While Black Swan says it's 2017, the Versions tab reveals it received a 2020 update to make it compatible with 5.2 (and as far as I can tell, all 5.2 themes are compatible with 5.3). Though, I think I prefer how RayOff looks.