It does not seem to matter if free snap is on or off, Restrict Orthangonal forces you to start a line from somewhere on the x or y plane of the Relative Zero Point. This behavior is shared with (inherirted from?) Qcad, and departs from the Autocad convention. I know the way its been done for 40 years is not always right, but in this case the fixation on relative zero is limiting.
Try starting the line with Restrict Vertical/Horizontal turned off, then turn it on to finish the line. That's how I've been using it, anyway.
Another solution is to not use Restrict Vertical/Horizontal but hold down the shift key after starting a line. This constrains the line to 15° angle intervals so if you hold the cursor close to horizontal or vertical, you can place the endpoint vertically or horizontally from the start point.
- press SHIFT to set the second point, this enables 15° snap and gives exact horizontal/vertical lines too
- use the command line, set first point, then enter @100,0 - that sets the endpoint 100 to the right horizontally (because Y=0)
- or enter @100<90 - 90 is the angle and creates a vertical line
investing less than half an hour into Search function can save hours or days of waiting for a solution