How to scale a text box (frame) by value (I mean by reducing the % or value of width/height amount, not by dragging the node) and keep the text proportion (scale text inside by the same value)?
Nope.
How about drawing a box around your text then group together. Again remove the outline.
Thank you but I'm not sure how your suggestion should work. By "text box" I meant paragraph text.
The closest thing I can think of is to resize the Paragraph Text frame, then use Text>Paragraph Text Frame > Fit Text to Frame.
Yes, paragraph text. Select Paragraph, double-click rectangle tool, group both, remove outline. Now you can scale according and text will scale too. But maybe that's not what you're after either.