Sync of read-only shared folder has permission issues since many versions (Windows)

[AndyFx12]

⚠️ Before submitting, please verify the following: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I have searched for it).
• Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• I agree to follow Nextcloud's Code of Conduct

Bug description

Since many versions (I guess 3.10) successfull sync of our shared datas is broken. We've got ~80 GB with ~ 30000 files, shared to a group of employees.
This share is restricted to

• download and sync
• read-only
• share
  Seems to be a problem on Linux, too:
  [Bug]: Permission denied syncing "read only" shared folders #9488

On a fresh installed Windows 11 with current NextCloud Desktop (34.0.1rc1) sync of this files failes with permission WindowsError 5.

There are (I assume fully synced) temp files left:

This temp files have wrong permission on Windows-Filesystem - so they never could be renamed correctly:

Steps to reproduce

1. Install current NextCloud Client on Windows 11 (NTFS-Filesystem) and try described share-permissions from above:

2. Let them sync.

Expected behavior

A full and correctly named sync of my files.

Which files are affected by this bug

Every file, shared with read-only permissions.

Operating system

Windows

Which version of the operating system you are running.

Windows 11

Installation method

Official Windows MSI

Nextcloud Server version

34.0.0

Nextcloud Desktop Client version

34.0.0rc1

Did this occur after an update or on a clean installation?

Clean desktop client installation

Are you using the Nextcloud Server Encryption module?

No

Are you using an external user-backend?

• Default internal user-backend
• LDAP or Active Directory
• SSO - SAML
• Other

Nextcloud Server logs

There are no related logs.

Additional info

Workaround:

• changing permission on Windows-Filesystem
• delete issued folder
• change permissions on server to full-access
• sync
  But I really need "read-only" restriction!

Partially logfile:
20260614_1126_nextcloud.log.0.gz