wx.ready(function () {      //
    wx.updateTimelineShareData({ 
        title: '', // 
        link: '', // JS
        imgUrl: '', // 
        success: function () {
          // 
        }
});

take a look at Wechat jssdk development documentation

landlord, have you solved your problem? I have encountered the same problem

official account has not been able to achieve the function you mentioned. Oh,

sharing must be triggered actively by the user, and can only guide the user to click on the upper right corner to share.
in addition, the shared image must be a link, and you have to find a way to upload the base64 data generated by the canvas image to the file server to generate a link.

I said I could do it.

1. canvas screenshot is transferred to the server, and the server provides a picture link
The
2. front end receives this picture and updates the Wechat sharing settings on the current page
3. A pop-up message prompts the user to share