[Bug]: Synchronization/?2-thread Checksum Checking? freezes the UI.

### ⚠️ 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

The UI isn't separate from the synchronization/checksum checking thread, if there are files and folders present then the synchronization freezes the UI.
...

### Steps to reproduce

1. Install nextcloud.
2. Synchronize(turns out later for whatever reason couple folders are empty).
3. Uninstall nextcloud.
4. Install nextcloud back.
...

### Expected behavior

Just you know being able to use the app, before it verifies 200GB worth of data.
...

### Which files are affected by this bug

- irrelevant

### Operating system

Windows

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

Windows 11

### Package

Official Windows MSI

### Nextcloud Server version

- not my server

### Nextcloud Desktop Client version

3.13.3

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

Updated from a minor version (ex. 3.4.2 to 3.4.4)

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

Encryption is Enabled

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

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

### Nextcloud Server logs

_No response_

### Additional info

_No response_