Xiaomi is notorious for their aggressive battery optimization so we have to exempt Manage SPIN from this aggressive battery optimization. Thankfully, Xiaomi does provide a method to have the permissions "stick."
- Settings > Advanced Settings > Battery manager > Power plan is set to Performance
- Device Settings > Advanced Settings > Battery Manager > Protected apps – your app needs to be Protected
- Device Settings > Apps > your app > Battery > Power-intensive prompt and Keep running after screen off
- Settings > Additional Settings > Battery & Performance > Manage apps’ battery usage and here:
- Switch Power Saving Modes to Off
- Choose the next options: Saving Power in The Background > Choose apps > select your app > Background Settings > No restrictions
App battery saver
Security > Battery > App Battery Saver > your app > No restriction
As per this article by Xiaomi: Open Security app > Permissions > Auto-start Enable Autostart for desired apps.
When you open recent apps tray, drag your app downwards – it will be locked. So even if you clear recent apps it will not clear from the background. Drag downwards again to clear your app from the background.
Tips from https://dontkillmyapp.com/xiaomi