IL2CPP build crashes on launch when returning an object with custom method

Unity: IL2CPP

Backport

2021.3.X

Fixed in: 2021.3.7f1

Reproduction steps:
1. Open the user's attached project
2. Built and Run it for IL2CPP

Expected result: The build finishes and launches
Actual result: The build finishes, but it crashes on launch

Reproducible with: 2021.2.0b8, 2021.3.2f1
Not reproducible with: 2019.4.39f1, 2020.3.34f1, 2021.2.0b7, 2022.1.0a1, 2022.2.0a13