I've seen Microsoft Visio used pretty often in larger/non-tech companies.
I opt for https://draw.io if I need a quick diagram personally (it's a big plus that you can guarantee the recipient has access since it can be opened from the browser version).
I’ve made mostly due with Google Doc with Google Drawings. They are editable, so better than a picture. However, the canvas has limited size, smaller than a doc page. It forces multiple drawings for a single flow sometimes.
I need to collaborate with other people and because of COVID we are doing everything remote. Also modifications would be hard and time consuming with pencil and paper.
It is free and online. I can draw diagrams that I used to draw with Visio but I don't have to install software and can use it from anywhere.
I can export the documents to my local machine as a master file (e.g. file type is *.drawio) or can export them as an image (e.g. JPG, PNG, etc.)
There are lots of subjects that you can turn on (also free) ranging from architecture to electronics.
I can usually find what I need or something that works well enough for my simple needs.
I can also use it kinda like a white-board in screen-sharing meetings.
Though - looking at other comments - yEd looks pretty powerful. I'll have to check it out.