Question: Are you sure?
If you are for some reason, get EiffelStudio (at least 23.09) from here. Follow the instructions to install EiffelStudio and set the right environment values that it wants. At this point, you should have a working compiler and build tooling.
To run a particular day's solution, first run ec -config dayXX/dayXX.ecf,
which should create a folder along the lines of EFIGENs/dayXX/W_code. cd to
that folder and run finish_freezing [another tool for Eiffel] to generate the
actual executable from the generated C code. The executable should be named
aoc2023-XX.
Finally, run the executable and pass in the path to the input file for that day.
Congrats! You made it!
Like GUI IDEs and don't want to run code directly? Finish installing the IDE completely, and pray I didn't mangle the configurations too much for it. Godspeed, you'll need it.