Enable "G-sync for windowed and full screen mode" create mouse lag (This is reproducible on two different computers, both Nvidia GTX 1080 and RTX 2080)
Enable "G-sync for full screen mode" solves the issue.
Disable hardware acceleration in Spotify solves the issue.
Thanks for letting us know. We're looking into this and will get back to you as soon as we have any updates. In the meantime, if you're experiencing this, make sure to reinstall the app, and if that doesn't work let us know the following: