下面的代码我朋友试了有用

 // 为了每次都读取最新的启动图，所以要在有缓存的时候清除缓，
 - (void)removeLaunchScreenCacheIfNeeded {
    NSString *filePath = [NSString stringWithFormat:@"%@/Library/SplashBoard", NSHomeDirectory()];
    
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
     NSError *error = nil;
     [[NSFileManager defaultManager] removeItemAtPath:filePath error:&error];

     if (error) {
          NSLog(@"清除LaunchScreen缓存失败");
        } else {
          NSLog(@"清除LaunchScreen缓存成功");
        }
     }
 }

Xcode11 & iOS13 LaunchScreen.storyboard 启动方案