Not sure why you’re being downvoted. The ability to upload your own songs to the cloud is something I so wish Spotify had, it really is great.

It's one of the reasons why I was using Groove. I'm going to keep the app to be able to play these songs.

The song limit is really better in Apple, but you are able to add your own music in Spotify. To listen to it in other devices I had to download it in them.

From what I remember having spotify, the only way to add your own music is to add it to a playlist from your computer, and then sync that playlist locally, so it basically just uses Spotify as a relay for your music on your computer. I'm assuming Apple is like Google Play Music, which lets you add albums and songs to your library that appear the same way as the streaming ones (within your albums/artists/etc) and don't need to be synced locally.

By "locally", you mean "in the same network"; I don't believe you have to connect your device physically to the computer.

That download process is outside of Spotify, right?

With Apple Music, I believe, it's available across all your Apple music supported devices.

It is inside the app. It is the same process that you do to make playlists available offline. I only did that from my laptop to an android phone, I don't know if it works in all clients.

Spotify kind of lets you add your own music, but only to playlists, not to Your Music. I don't get it.