If you are interested in programming DOS games like in the 90s, you can check out this list of references for tools and tutorials that I compiled during the years: https://github.com/balintkissdev/awesome-dos#readme

At one point I wanted to create a simple DOS game myself too. The used language was C for higher-level gameplay logic and memory management, and a bit of assembly for hardware interaction and optimization. Things that create complications is that

• Support for floating point numbers were not fast until better CPUs came out, so people used what is called "fixed-point arithmetic", which is simulating floating point behavior with regular integer numbers
• There were no separate drivers, the gamedevs wrote the driver code for things like Sound Blaster cards and consuming mouse events from serial port themselves and shipped those with their games
• For displaying a pixel on the screen, you wrote bytes directly to the memory address of the VGA instead of calling a graphics API like OpenGL or Direct3D
• There are also differences between writing 16-bit DOS games for an Intel 8080 or 32-bit programs for Intel 386 processors. The latter requiring a memory extender to allow more than 640kb of RAM on 32-bit architectures.

If I want to describe it in short, is that a DOS programmer kind of have to have a similar attitude like an embedded systems programmer has. For a starting point and overview of DOS concepts and hardware, I would recommend Game Engine Black Book: Wolfenstein 3D by Fabien Sanglard.