[Bug]: NC 4.0.4 not able to sync with not empty folder

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- [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

I have a 5 TB Nextcloud at hetzner.com. I work with linux Mint 22.2 and 2 devices work fine with the appimage 4.0.4 instead of the appimage 3.13.4
First: the endless sync failure is fixed now. That works.

But: On my 3rd device a have a nextcloud folder with 2.1 TB synchronized and here with the setting of the 3.13.4 the 4.0.4 crashes at start. So i tried to make the configuartion new for the 4.0.4. Here is a bug: The Nextcloud Appimage 4.0.4 accepts only an empty folder. But my folder on the device is full with 2,1 TB synchronised 5min ago with the 3.13.4.

Here is the setting of the 3.13.4

### Steps to reproduce

Try to synchronise local files with a nextcloud - the setting refuses a not empty folder
...

### Expected behavior

I want to select a previous synchronised folder from another version

### Which files are affected by this bug

complete Folder

### Operating system

Linux

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

Linux Mint 22.2

### Package

Official Linux AppImage

### Nextcloud Server version

31.0.10

### Nextcloud Desktop Client version

4.0.4

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

Fresh desktop client install

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

Encryption is Disabled

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

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

### Nextcloud Server logs

```shell

```

### Additional info

_No response_