@Thales750
Honestly back when I did this work I used Google Sheets as the back end. Partly this decision I made was due to Appsheet's licensing structure at the time, which they have changed, like...5 times since then. At the time they were just getting started, and really appreciated their customers more - I believe if your back end was Sheets at that time, licensing was free if you had a small # of users, which I did. I remember days when I actually got support emails back directly from Praveen, one of the founders, not sure if he still there.
Now their licensing structures have changed, but also more powerful - sql server is totally an available back end. I have no knowledge or skill in how to "open up" a sql server to that type of access, so I haven't used it like that, but they connect to a lot of great db's.
Appsheet's capabilities are also 100x what they once were. When I was using it they didn't even have push notifications! So I guess con razon now they charge a bit more.
I used to do some work for a major construction consulting
firm. We used access, sql server and some web programming platforms a lot. I don't remember mobile apps being a part of it, but then again, like you said - 'mobile device' which is more expansive. I guess they just used laptops, as well as perhaps tablets that ran MS Programs (surface etc).
Appsheet's web-based dev is really awesome - and loads of fun. live simulator on the right hand side of the screen to simulate any screen size.