All you have to do is, install the UserCenter.
I extracted the following apps from FlymeOS 22.214.171.124 Test, using Titanium Backup. From my MX5, yet those apps should work on the Pro 5 too.
Apps and Versions:
- AppStore 5.0.16
- Browser 3.2.0401
- Themes 5.0.4
- UserCenter 5.0.6
Link: Chinese Stock Flyme Apps
These files are on my private google drive. You may install these on YOUR OWN RISK.