Reproduction steps:
1. Open the attached “repro-cts-unity-webgl.zip” project
2. Build and Run for WebGL (File > Build and Run)
3. In the Player press the “Start” button
4. Observe the text next to the button

Expected result: “Is Cancelled: True” text is visible
Actual result: “Is Cancelled: False” text is visible

Reproducible with: 2021.3.45f1, 2022.3.50f1, 6000.0.23f1, 6000.1.0a1

Reproducible on: Windows 11, macOS 15.0.1 (M1 Pro)
Not reproducible on: no other environment tested

Note:
- Does not reproduce in the Editor or Windows build