I know about sizing a text box in mobile in order to keep the desktop version constant. In the scaling bar, the starting value is 50, what does that represent?

When editing inside the text box, is there anything that does NOT affect the desktop:  font, spacing, styles, line feeds… anything?

I recall reading something about holding down ctrl for making something unique to mobile, what was that referencing?

I understand that scaling anything seems to NOT affect the desktop. This includes sizing sections. Is there a chart somewhere that lists all the things that do NOT affect the destkop?