I've been wondering — is there any other custom locker app that supports music controls on lockscreen for Spotify just like the android's default one?
I tried only Go Locker - this one, doesn't do Spotify.
Most custom lock screens allow adding widgets... can you not just add the Spotify widget to the lockscreen?
You may have to enable adding widgets in the lockscreen settings.
I found ZUI Locker which has native music controls, it works for Spotify and other music apps (podcasts) so it's awesome.
Also dodol locker allows widgets, actually, only one widget so not perfect not to mention that widgets are quite battery draining, but it's ok. But besides that I couldn't find anything else.