Thanks, Walt. One of the portions that I expected to be in a serif font is here, with no mention of sans-serif:
<text id="titletext" transform="translate(802.5, 44)" font-size="50px" class="title-text noselect" style="display:block;font-size:50px;height:auto;overflow-x:visible;overflow-y:visible;white-space:nowrap;width:auto;perspective-origin:0px 0px;transform:matrix(1, 0, 0, 1, 802.5, 44);transform-origin:0px 0px;user-select:none;fill:rgb(0, 0, 255);text-anchor:middle;">Hello World ssh</text>
I will add an explicit font-family="serif" in my original. I have also worked around the rgba display error in inkscape and others by switching to rgb and an explicit opacity=0.5 or whatever.
6) I think there is still a clipping issue in Affinity (and inkscape), not seen in the original file, but seen in the attached svgtop(6).svg file. The black horizontal lines headed off the the left edge should be clipped at the left of the main white area, as seen when opening this file in a browser. Possibly related to nested svg regions, but apparently only clipping to the outermost one. There should also be a light yellow background outside the main white area: see a browser display of this. /dick