There are currently five methods to upload a ready file to Kindle. The book will work regardless of the chosen method.

Just drop MOBI to Documents folder on your Kindle. For older Kindle models, check auto cover upload.

Both USB and SSH upload is working correctly. In both cases, covers will be displayed in library view on newer Kindle models.

As long MOBI is smaller than 50MB this method should work correctly.

Upload it like a normal book.

Just use normal methods available for your device.