Here are the 4 steps to get Boomerang to work with Xiaomi devices:
1. When Boomerang prompts for the Accessibility Permission, grant it.
2. Ensure that Boomerang is allowed to Autostart. Find Autostart in the Xiaomi device’s Android Settings and add Boomerang as an App that is allowed to Autostart.
3. Ensure that Boomerang is an App that is not optimized by the Xiaomi Battery Saver
4. Ensure that Boomerang has all the 6 permissions.