TamperMonkey is a userscript manager that allows users to create JavaScript scripts that can be remotely loaded by the extension to change the functionality of a site that they visit. The author of the Tampermonkey Chrome extension has stated that this proposed change would prevent his extension from working as the ability to load remote-scripts is part of its core functionality. Google has not directly addressed Jan Biniok’s concern in the Google Groups thread, but have provided the following statement to BleepingComputer.
Source: https://www.bleepingcomputer.com/news/google/tampermonkey-may-be-the-next-victim-of-googles-chrome-manifest-v3-changes/