The good news is, if you have a large enough low-dpi display, and you make the window big enough, the automatic integer scaling settings will kick in, and the pixels themselves will be displayed larger. This can be forced via the preferences app (under the display options). If you screw this up, then restart LisaGUI while holding the shift key to reset the scaling settings.
EDIT: Unrelated to this, there are a couple minor bugs with PWAs on iOS relating to the positioning of the canvas. These can be resolved by rotating your device to a different orientation and then rotating it back to the original position... but this is annoying.
EDIT 2: To close windows, just double click the icon in the titlebar! This "collapses the window back into an icon."