Extend an existing polyline?

Cesium does not works on Safari 13.x - throws an exception that browser does not support WebGL

It’s possible that support for WebGL is turned off in your Safari browser. Please reference this guide for how to turn WebGL support on (see the Safari section): https://support.biodigital.com/hc/en-us/articles/218322977-How-to-turn-on-WebGL-in-my-browser#h_01EJW3MN2N79NA97TRW4RC849Q

Please follow up if that did not work for you.