How to reproduce:
1. Open the attached “IN-86483” project
2. Open the “test.uxml” file in the Assets folder
3. In the UI Builder window Hierarchy section select “CustomControl.cs”
4. In the Inspector window Attributes section click on “Select Type…” near the Type attribute
5. In the “Select Type…” window search for “System.Boolean”
6. Observe the “Select Type…” window

Expected result: “System.Boolean” type is found
Actual result: No type is found

Reproducible with: 6000.0.28f1, 6000.1.0a5
Could not test with: 2021.3.46f1, 2022.3.53f1 (Type attribute does not exist in the UI Builder)

Reproducible on: Windows 11
Not reproducible on: No other environments tested