[Bug]: NC25 not working with disabled Theming app

[Rello]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• Nextcloud Server is running on 64bit capable CPU, PHP and OS.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

when the theming app is disabled, NC is loaded without css.
Error "Could not find initial state background of theming" in browser console

Steps to reproduce

1. Apps -> disable Theming app
2. Refresh Page

Expected behavior

Avoid the feature to disable the Theming app, when its that important

Installation method

No response

Operating system

No response

PHP engine version

No response

Web server

No response

Database engine version

No response

Is this bug present after an update or on a fresh install?

No response

Are you using the Nextcloud Server Encryption module?

No response

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

No response

List of activated Apps

Theming

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

[genma]

I've the same issuses a written a blog post in French with some screenshot https://blog.genma.fr/?Nextcloud-25-l-application-theming-casse-l-affichage-des-CSS

[AndyScherzinger]

Looping in @PVince81 and @juliushaertl

[PVince81]

and @Pytal

[Pytal]

Some dashboard js depends on theming to adjust the header

Tracking in #33969

[nickvergessen]

Since the theming app now also hosts the accessibility settings, should we force enable it?
Feels weird that an admin can decide to punish people for their accessibility lacks by disabling an app they just don't need themselves?

[szaimen]

WIP here: #34609 however I didn't test yet what happens if you disable the app and upgrade to this branch.