[Bug]: Nextcloud desktop appears in light mode on dark Debian Xfce

### ⚠️ Before submitting, please verify the following: ⚠️

- [x] This is a **bug**, not a question or a configuration issue.
- [x] This issue is **not** already reported on Github (I've searched it).
- [x] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

Nextcloud desktop appears in light mode on dark Debian Xfce

### Steps to reproduce

install Debian GNU/Linux 12 (bookworm)
configure Xfce
run Nextcloud-4.0.1-x86_64.AppImage

### Expected behavior

Nextcloud should appear in dark mode

### Which files are affected by this bug

None

### Operating system

Linux

### Which version of the operating system you are running.

Kernel: Linux 6.1.0-41-amd64

### Package

Official Linux AppImage

### Nextcloud Server version

31.0.10

### Nextcloud Desktop Client version

4.0.1

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

Updated from a minor version (ex. 3.16.1 to 3.16.2)

### Are you using the Nextcloud Server Encryption module?

Encryption is Enabled

### Are you using an external user-backend?

- [x] Default internal user-backend
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell

```

### Additional info

_No response_