What most seem to do is to use an application like Godot or Unity to build the engine in step 2. You do not have to start from scratch you know. Those things ar

What most seem to do is to use an application like Godot or Unity to build the engine in step 2. You do not have to start from scratch you know. Those things are more or less toolkits for building your actual game's engine. Not like the more specific game engines that you might think of if you are older and remember game engines last century. Depending on what game it is I can see someone using something like Raylib to build their engine instead. The abstraction level there is about the same as Godot. You get high-level API:s for a large number of things and support for many platforms (far more than what Godot or Unity supports). What you do not get is a GUI for building scenes or editing scripts. Starting from a lower level with something like SDL sounds like something more suitable for hobby projects, like coding a game in TIC-80 or writing a 16-bit DOS game in FreePascal or other hobby-activities (things that I enjoy). Fun, but probably almost never a good idea for a business.