[Bug]: UI flickering and unresponsive menus in Nextcloud Desktop 3.3.0 (AppImage) on Linux and Windows

[nunopequito]

⚠️ 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've searched 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

After upgrading to Nextcloud Desktop 3.3.0, the application UI becomes unstable:

Menus flicker continuously
UI elements are difficult or impossible to click
The application becomes unusable

This happens consistently and prevents normal interaction with the client.

Steps to reproduce

1. Launch Nextcloud Desktop 3.3.0 (AppImage on Linux or installer on Windows)
2. Open the main window
3. Try to open or interact with the menu
4. Observe flickering and inability to click

Expected behavior

Menus and UI should be stable and fully clickable.

Which files are affected by this bug

Nextcloud-33.0.0-x86_64.AppImage

Operating system

Linux

Which version of the operating system you are running.

Mint 22.3

Package

Official Linux AppImage

Nextcloud Server version

33.0.0

Nextcloud Desktop Client version

33

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

Updated to a major version (ex. 3.16.3 to 3.17.0)

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

Additional info

• Issue occurs on both Linux and Windows, suggesting a cross-platform regression
• Problem affects UI rendering and input handling (not sync or network)
• No browser issues with the same Nextcloud server
• Running previous versions resolves the issue immediately