The best place to find simple SDL3 tutorials at the moment is examples.libsdl.org, which offers small programs that each demonstrate one feature of the library. Most of the examples are 100-300 lines of C code. There are also simple-but-complete games and apps in the demo section, which are slightly larger (closer to 500 lines of C code), but more comprehensive.
The examples website runs each program directly in the web browser, and has a popup tab to show their source code, with all symbols linked to their wiki pages for easy research.
And, of course, all of the examples are included in SDL's source tree, in the "examples" directory, for you to tinker with and explore.
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