[Bug]: Choosing photos directory gets stuck if large number of files (filepicker)

⚠️ 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

If the directory contains a large number of files, the file picker dialog never completes. The problem is we don't filter for the mimetype in the WebDAV call, but only after getting the entire directory listing.

Steps to reproduce

1. Have a lot of files in a directory
2. Open the file picker (e.g. in the Photos app to choose the directory)
3. Stuck

Expected behavior

Show folders.

Installation method

Community Docker image

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.0

Web server

Apache (supported)

Database engine version

MySQL

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

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

What user-backends are you using?

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

Configuration report

No response

List of activated Apps

Irrelevant

Nextcloud Signing status

No response

Nextcloud Logs

No response

Additional info

No response

Start by tracing the file picker directory listing and the WebDAV call it uses when choosing a photos directory. Check where the mimetype filter is applied, then verify that filtering happens in the request and that a large directory completes while showing folders.