This is the next step towards a proper KF5 based release.
Not to rain on the Amarok devs parade, but KF 6.1 was just released. Wouldn’t it make more sense to start targetting KF6 instead?
Work on a KF5 release had already started years ago and was mostly completed. With the recent revival of the project, it made sense to take things one step at a time and complete the KF5 port first.