How do I know WHAT I have to learn ? (Flutter)

I am currently working on a Video App but I don't know how to make a flutter app that can edit videos like trim them, make them of a specific aspect ratio (like add extra blurred space to fill up), add filters or do other stuff with video

Like I don't even know if these things are possible with flutter, I have no idea what to learn to implement this and googling didn't help either

I know there are libraries for these features but what if I wanna learn to make these stuff on my own because I don't wanna be a dependent developers who depends on other people for libraries I want to learn to write these on my own

I might not have been able to explain myself through this question, sorry for a vague question but pls don't close it, I really need to know the answer.

I tried googling, I tried looking up documentation but 'twas not of much help

1. You must know on which platform you want to have the application
2. It depends on the platform you choose to learn.
3. Flutter is good at creating a single code base for multiple platforms at once, but unfortunately there are things it can't do and must be done in the language of the target platform.

If the app is for Android and IOS, it would be better to learn Jetpack Compose and Swift,

Flutter will save you time in the future, but you would have to learn all three including flutter