Yes, my understanding is that Theodore Gray invented the "computational notebook" for Mathematica in the 90s. Here is the best writeup of the history of the notebook that I've ever read. https://www.theatlantic.com/science/archive/2018/04/the-scie...

quick look at Wikipedia shows Mathematica: "Initial release June 23, 1988;"

Mathematica took at least a year or more to write.. so that goes back perhaps to 1986.. 90s is way off...

Looks like a yes according to this page at least: https://en.wikipedia.org/wiki/Notebook_interface

MathCAD had a WYSIWYG notebook in the same time frame, late 80s, but I have no idea which of them was first with it. It's possible that it was neither.

Mathematica certainly pushed the Notebook format as a fundamental feature, with WYSIWIG math that no one else had ..."Invented" is pretty hard to say honestly, but the popularization and technical polish, absolutely yes