possibility to create a button to switch between sync & non sync lyrics

[monkey]

perhaps it's already possible, but i didn't found how...

[Mayibongwe]

You are right in that it's currently not possible.
Whenever a track's lyrics has valid timestamps, it will have synced lyrics displayed irrespective of whether or not there's other unsynced lyrics stored in the equivalent tag.

I understand this is a wishlist section free for all, but could you explain why you would want to keep on switching between the two?
IMO, It's either you're a fan of synced-or-unsynced lyrics - I haven't heard of an inbetween preference till now.