The APK is already signed (v1 + v2 + v3). That warning is just a false alarm from MT Manager's built-in signature check (because the APK is 1.27 GB and uses a 4096-bit custom key).
How to install it:
In that exact popup on your screenshot, simply tap "INSTALL DIRECTLY" on the left.
Alternative: Install the APK using your phone's normal Files / Downloads app instead of MT Manager (or turn off "APK installation verification" in MT Manager's settings).
Important: If you already have an older version of Sifu installed on your phone, uninstall the old Sifu app first before installing this one (otherwise Android will block the installation due to different signatures).
(Note: If you edited the APK yourself inside MT Manager, tap the APK in MT Manager → Function → Sign APK first.)
hlo
