Either the APK you're trying to install is corrupted or it has something to do with your ROM, I guess
新功能
4.5: • Added a setting to disable opening .apk files via SAI • SAF fixes for Android 11 • Added warning when installing huge (>150MB) apps
4.4: • Fixed in issue where system suggested SAI when opening any type of file • Added Sui support for Shizuku Installer
Legendary SAI update Pog 4.3: • Support for opening .apk files via SAI • APKM support (only for the unencrypted .apkm files) • Installer Pro mode is now enabled by default • Config splits shouldn't be marked as Unknown anymore