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.
consumePath = typeof consumePath !== "undefined" ? consumePath : true;
    const ctx = this.ctx;
    const strokeColor = this.current.strokeColor;
    
    
    ctx.globalAlpha = this.current.strokeAlpha;
    if (this.contentVisible) {
      if (typeof strokeColor === "object" && strokeColor?.getPattern) {
        const lineWidth = this.getSinglePixelWidth();
        ctx.save();
        ctx.strokeStyle = strokeColor.getPattern(
          ctx,
          this,
          ctx.mozCurrentTransformInverse,
          PathType.STROKE
        );
        
        ctx.lineWidth = Math.max(lineWidth, this.current.lineWidth);
        ctx.stroke();
        ctx.restore();
      } else {
        const lineWidth = this.getSinglePixelWidth();
        if (lineWidth < 0 && -lineWidth >= this.current.lineWidth) {
          
          
          ctx.save();
          ctx.resetTransform();
          ctx.lineWidth = Math.round(this._combinedScaleFactor);
          ctx.stroke();