Package Manager's Invalid or Missing Signature pop up window is rendered with artifacts

Steps to reproduce:

1. Create a new Project
2. Open Package Manager Window
3. Press the + button and select the "Install package from Tarball..." option
4. Select the attached package in the file browser
5. Observe the Invalid Signature pop-up window once it appears

Actual results: Pop-up window is rendered with artifacts from other Editor Windows. When the mouse cursor is moved inside the pop-up, the window will change its size. If the Vulkan graphics API is used, the window will eventually be rendered properly. If the OpenGL graphics API is used, the window will not be rendered properly and trying to move the pop-up will result in other Editor windows becoming uninteractable and rendered in solid black

Expected results: The Invalid / Missing signature pop-up window is rendered correctly as soon as it shows up, and it does not affect other Editor windows

Reproducible with versions: 6000.3.0a5, 6000.3.3f1, 6000.4.0b3, 6000.5.0a4

Can’t test with versions: 6000.0.65f1, 6000.3.0a4 (Invalid/Missing signature pop-up window was not yet available)

Reproducible on (OS): Ubuntu 24.04 (OpenGL, Vulkan)

Not reproducible on OS: macOS 26.1 (Metal)

Notes:

• When using Ubuntu 24.04 with Vulkan, the Signature pop-up window will only be rendered properly if the user moves the mouse cursor inside the pop-up window.