I am a beginner with Nextcloud, so it’s possible that I may have overlooked some solutions. I would like to know if it’s possible to enforce accessibility settings globally for all users. Specifically, I am interested in the Dark mode. I would like to have the Light mode active by default, meaning that even if the Dark mode is enabled system-wide on a PC, the browser will always display the white mode. Since I have a Managed Nextcloud plan (with IONOS), I probably have limited ability to modify the CSS/source code.
Afaik no. You can enforce the theming options like logos, backgrounds and colors, (Administration Settings → Theming → Disable User theming), but not the accessibility settings.
Also I don’t think it makes sense to force certain accessibility settings to all users. Every user should be able to choose which mode he or she is most comfortable with. And with the High Contrast Mode and the Dyslexia Font, there are also settings available that are more than just an aesthetic preference for people with disabilities.
That’s possible on a per user basis. Just go to the “User Settings” → “Appearance and accessibility” and set it to “Enable default light theme” instead of “System default theme”
Then, of course, it is also possible that the provider has further customized the instance. If not all of the options I have described above are available on your instance, you will need to contact the provider.