With a lot of sweat and tears I can make it disappear.

SwiftUI Charts is a great framework.  But there are some sharpe corners that can cut you like a knife.  Here is an example - the dreaded double (inner & outer) boarder that comes when you inset the label values of the Y-axis.  In many charts this is not going to become an issue because you will have the typical lables on the outside.  But if you want to maximaize the plot area and use inset labels... there is a good chance you will see this inner and outter boarder  (see my example's right side).

Like magic I can make that disappear with one comment.

Removing the AxisTicks from the AxisMarks removes the outter spacing and the boarder lines collapse (just like Quantium Reality) into the same line..

How do I fix the plot bounds chopping the plotted black dot?

This is the trick for padding on the X-axis:  it's way down deep in the Chart modifiers.

.chartXScale(domain: xDateDomain, range: .plotDimension(startPadding: 5, endPadding: 5))