Sioyek developer here, we don't have the exact feature you ask for, but we have an alternative.
Instead of modifying the PDF file (which kind of is against the point of PDF files in the first place, the point is the file looks the same in all devices) we have a ruler which can automatically highlight the line being read. If the line is larger than the window, then we move horizontally so the next part of the line is shown. If the line is such that it is larger than the current window but is smaller than the next horizontal movement, a red notch is displayed in the ruler which marks the location of the line which will be moved to the leftmost side of the window.
> Instead of modifying the PDF file (which kind of is against the point of PDF files in the first place, the point is the file looks the same in all devices)
I, as a reader, don't care about this. I want the document to be the most readable on all devices.
Instead of modifying the PDF file (which kind of is against the point of PDF files in the first place, the point is the file looks the same in all devices) we have a ruler which can automatically highlight the line being read. If the line is larger than the window, then we move horizontally so the next part of the line is shown. If the line is such that it is larger than the current window but is smaller than the next horizontal movement, a red notch is displayed in the ruler which marks the location of the line which will be moved to the leftmost side of the window.
I know I explained it poorly, here is a video which should clarify: https://www.youtube.com/watch?v=ZYUYMhvwN3U