The short answer is no, the Spotify flatpak is not maintained by Spotify developers.
The long answer is that I don't even think the snap package is maintained by Spotify? I think it's more officially sanctioned by Spotify?
In all actuality the Spotify desktop app really isn't supported officially at all on Linux and not maintained as it should be. I haven't used it on Windows or Mac but if it's anything like the Linux version as far as how crusty and generally low quality it is it's pretty shameful as a whole.
The flatpak as part of it's build process actually downloads the snap and uses the containing binaries and re-wraps it up as a flatpak while also fixing/working around a few bugs in the official app inside the flatpak wrapper.
The flatpak is going to give you a better experience as less things are broken. (there are A LOT of YEARS OLD outstanding bugs in the Linux version)