I spent two weeks trying to curve text in various animation softwares and failed. It was frustrating at first. I failed many times in Synfig, until I tried it again today. I figured out the parametre settings. The result is what I got in the video link below. I only made the video just today.
I first did text in Inkscape, coverted text to paths before exporting it in SIF format.
In Synfig, I went to New Layer > Distortion and chose Curve Warp Layer. In paramatre panel, I ticked off “fast” so to get a nice clean look.