The source code to most of my projects are available on Github, predominantly in Unity/C#. Code can be reused for all purposes except commercially.
A lot of people asked me on Discord what I use to create my games, so I'll list them here:
All my current games are made in Unity with C#. The engine is robust, good for both 2d and 3d games, and relatively friendly to beginners with only a little bit code knowledge. I learned most of the engine through playing around with things and looking at YouTube tutorials.
Making any sort of 3d games requires some basic knowledge of modeling. I've never made anything fancy, and I usually just use blender to make certain 3d shapes and some guns/tanks for Retro Combat (currently I use models from the Unity Asset Store and modify them in blender).
Probably the most important for any application development. I make all my 2d sprites, UI icons, game logos, and screenshots here. Illustrator is also good for original 2d vector art.
Most of my server code and miscellaneous code are done in python, as it is very versatile and doesn't require compilation. Some networking packages I use in python include FastAPI, SQLAlchemy, and Starlette (websockets).
MySQL is a database system I use for my games' account systems and community maps. Code that works with MySQL is mostly in python with SQLAlchemy, and I set up the tables and databases using MySQLWorkbench.
Linux Servers (Cloud Services)
I use Aliyun (Alibaba Cloud) and Huawei Cloud for my linux servers, but have also tried Google Cloud and AWS. Chinese services like Aliyun and Huawei Cloud are the cheapest, and Aliyun provides servers in the US. For comparison, Aliyun offers a 2gb ram + 20gb hard drive + 1mbps server for only $150 per year, and it can get as low as 1/3 of that price with sales. I put my main server in Hong Kong so the ip is not blocked by the Chinese firewall and thus Chinese users (if you want to use domains you must also register with the Chinese government to get it unblocked), which makes ping quite a bit higher.
Tutorials on how to use the Linux console are everywhere, so I won't elaborate on that. Use SSH to connect to the servers, install python and the packages above (using pip), and you can run the service. I also recommend getting a domain name so it's easier to remember AND you don't have to update your app every time you change a server.