I want to find a graphic application that can draw basic workflows with mathematical expressions. For example, I want to draw something like the following figure from "Implementation and Optimization of Differentiable Neural Computers" by Carol Hsin.
Photoshop and InDesign could do some of that. I am not sure of fonts being mathematical, so see if you can find 3rd-party fonts for the same. Adobe Illustrator is used for vector graphics extensively.
The industry-standard vector graphics software is used by millions of designers and artists to create everything from gorgeous web and mobile graphics to logos, icons, ..
Autodesk SketchBook can also help draw basic shapes rectangles, lines.
Same for https://draw.io
I'd still add LaTeX as an option. You shouldn't be scared of it.
https://www.overleaf.com/learn/latex/LaTeX_Graphics_using_TikZ:_A_Tutorial_for_Beginners_(Part_3)—Creating_Flowchartsgives an introduction. Use templates given on that site to start drawing. Use https://tex.stackexchange.com/ for reference or asking doubts.
https://tex.stackexchange.com/questions/168314/how-to-use-latex-commands-to-draw-a-flowchart gives you a working solution too.