The difference between a scatter graph and a line graph is that the x-axis should be mathematical. Ie if the X data points are 1,2,4 , the '4' should be 2 intervals away from the '2'. On a line graph, they would be next to each other and equidistant to the '1' and '2'.

When the x-axis column of data is number, it works.

I just tried twice when the x-axis column of data is formatted as time. Ie 1:00:00 = 1 hour, 2:30:00 = 2hours 30 minutes, etc. In this case, when selecting a scatter graph zoho sheet gives me a line graph, where the x-axis is not scaled to the value of the datum but rather one point per row.

Here's a public zoho sheet I made and shared that shows the difference.

screenshot attached.