Memory from the last exited managed thread is not freed when IL2CPP is used

How to reproduce:

1. Open the attached project “IN-150912”
2. Ensure that IL2CPP is selected as the Scripting Backend in “Project Settings → Player → Other Settings”
3. Build and run the project
4. Press ‘Space’ in the Player
5. Observe the payload status text at the top of the Player

Actual result: Payload 3 shows “alive = True”
Expected result: Payload 3 shows “alive = False”

Reproducible with: 6000.0.0f1, 6000.0.81f1, 6000.3.22f1, 6000.5.8f1, 6000.6.0b8, 6000.7.0a4

Reproducible on: macOS 26.5.2 (M4 Max)
Not reproducible on: No other environments tested