An empty rectangle is displayed over the main Unity Editor Layout when opening the project

Reproduction steps:
1. Open the user’s attached project
2. Observe the empty rectangle in the bottom left corner

Expected result: No empty rectangles
Actual result: An empty rectangle in the bottom left corner

Reproducible with: 2021.2.0a20, 2021.2.19f1, 2021.3.12f1
Not reproducible with: 2020.3.41f1
Couldn't test with: 2021.2.0a19 (Failed to load window layout popup), 2022.1.0a1, 2022.1.21f1, 2022.2.0b13, 2023.1.0a17 (Unity Editor opens in the Default Layout)

Reproducible on: Windows 11 Pro 21H2
Not reproducible on: macOS 12.6

Workaround: Reset Unity Editor layout to default, by clicking on Layout in the top right corner of the Editor and selecting “Default”