I would like to ask which software can I use to make such sketches. Please note that I am not looking for draw.io as it does not produce the same output.
Krita is a professional free, open source painting program for Windows/Mac/Linux. It is made by artists that want to see affordable art tools for everyone. You can work with photos or scanned images, or start with a blank slate. Krita supports most graphics tablets out of the box.
Krita is different from other graphics design programs in that it has pluggable brush engines, some supporting brush resources like Gimp brush files, others offering sophisticated simulation of real brushes, and others again offering color mixing and image deformations. Moreover, Krita has full support for graphics tablets, including such features as pressure, tilt and rate, making it a great choice for artists. There are easy to use tools for drawing lines, ellipses and rectangles, and the freehand tool is supported by pluggable "drawing assistants" that help you draw shapes that still have a freehand feeling to them.
draw.io is a free online diagram software for making flowcharts, process diagrams, org charts, UML, ER and network diagrams. draw.io is available for Windows. Mac and Linux. In many common Linux distribution that support the snap package format the drawio snap package can be installed with this command:
sudo snap install drawio
With draw.io you don't need to draw anything, just select an object from the left panel and drag it into the canvas. To change colors draw.io has a built-in color picker. In order to make this diagram I enabled the Network library which contains the laptop and phone shapes as follows: Click on More shapes… at the bottom of the left panel → Scroll down in the Shapes dialog to make sure the Network shape library is enabled → Click Apply.
Looks like it's been hand-drawn with a stylus.
If you have an iPad and an Apple Pencil, check the free app "Tayasui Sketches School", for example. The app can produce such graphs, in particular the watercolor effect, in 2 minutes.
Such apps are also available for Android and other OSs too. I think the important part is using a stylus/pencil, and any vendor will suffice.