How do i know a specific mime type for Android SAF?

Question

I'd like to save a file of my custom type (let's say .asf) using Android Storage Access Framework's ACTION_CREATE_DOCUMENT. What mime type should i pass to be supported at least default Android File manager and save on file storage? How about some more common extensions (eg. .hex)?

If i don't pass a type at all:

    fun saveFile(fromFile: File, fileName: String, mimeType: String, resultCode: Int) {
        inputFile = fromFile
        val intent = Intent(Intent.ACTION_CREATE_DOCUMENT).apply {
            addCategory(Intent.CATEGORY_OPENABLE)
            if (mimeType.isNotEmpty()) {
                type = mimeType
            }
            putExtra(Intent.EXTRA_TITLE, fileName)
        }

        context.startActivityForResult(intent, resultCode)
    }

i'm getting:

android.content.ActivityNotFoundException, No Activity found to handle Intent { act=android.intent.action.CREATE_DOCUMENT cat=[android.intent.category.OPENABLE] (has extras) }, , null)