I have reported this before. It is still just a silly bug.
Despite Rhino 8 supposed rewrite of print dialog it did not resolve it.
Steps:
-Draw a rectangle 210*297mm (a4 format)
-ctrl P
-set a4 print format
-set printing area by set window and select corners of the rectangle
-set margins to 0
-set scale to scale to fit
Reported scale is not exactly 1:1 and logically must be.
I dont understand how you dont seem to see the apparent problem.
I did the same thing in autocad (draw a4 rectangle and print the rectangle on a4 size format) and it correctly reports exactly 1:1 scale (model to print)
It is very important to trust the software. When software reports 297/297 is not 1 but 0,9981 something is wrong and you should try to find why that is.
I recently used print to export an svg and I remember thinking that there was something broken about scale to fit. I don’t remember specifics though.
Getting the scale right took a long time and often the preview would disappear completely. I figuered that I could use export as dxf instead, since I needed it in affinity and the dxf import works perfectly there.