This is a regression from #12864. The underscore is now too thin when the document is zoomed in.

URL: https://github.com/mozilla/pdf.js/files/2321540/issue6127.pdf
PDF.js 2.7.526: https://i.imgur.com/T4mIpct.png
PDF.js 2.7.510: https://i.imgur.com/nbwEpGT.png
Adobe Acrobat Reader DC 2020.013.20074: https://i.imgur.com/wDFBf3R.png

The screenshots were taken at 400% zoom.
canvas.style.height = `calc(${height}px * var(--viewport-scale-factor))`;
        this.annotationCanvasMap.set(id, canvas);
        this.annotationCanvas.savedCtx = this.ctx;
        this.ctx = context;
        this.ctx.setTransform(scaleX, 0, 0, -scaleY, 0, height * scaleY);
        addContextCurrentTransform(this.ctx);
        resetCtxToDefault(this.ctx);
      } else {
        resetCtxToDefault(this.ctx);
        this.ctx.rect(rect[0], rect[1], width, height);
        this.clip();
        this.endPath();
      }
    }
    this.current = new CanvasExtraState(
      this.ctx.canvas.width,
      this.ctx.canvas.height
    );
    this.transform.apply(this, transform);
    this.transform.apply(this, matrix);
  }
  endAnnotation() {
    if (this.annotationCanvas) {
      this.ctx = this.annotationCanvas.savedCtx;
      delete this.annotationCanvas.savedCtx;
      delete this.annotationCanvas;
    }
    this.restore();
  }
  paintImageMaskXObject(img) {