https://developers.weixin.qq.com/miniprogram/dev/api/canvas/wx.createOffscreenCanvas.html

开发者工具没问题，真机上，正式版，开发版都有问题，目前只测试了苹果手机每一个都有问题

const canvas = wx.createOffscreenCanvas({type: '2d', width: 400, height: 300});
  
console.log(canvas);