Matter-js use poly-decomp function. Sometime not work good. You can use alternative, try use google to find (matter-js decomp function alternation). https://github.com/schteppe/poly-decomp.js/tree/master/build
You can see on, i generate SVG background by modified poly-decomp.js https://mlich.zam.slu.cz/js-matter/js-bridge/bb-game.htm