Site: https://libsdl.org/

SDL is a collection of 3 libraries, i.e. 3 different versions: 1.2, 2.0 and
3.0, with significant differences between them. The game was made to use only
SDL 1.2 or SDL 2.0, but compatibility programs have been created between the 3
versions, so the game will run with all 3.

The libraries, compatibility programs and some download links are listed below.

SDL 3.0 and SDL 2.0:
-------------------

https://github.com/libsdl-org/SDL

"Simple DirectMedia Layer (SDL for short) is a cross-platform library designed
to make it easy to write multi-media software, such as games and emulators."

https://github.com/libsdl-org/SDL/releases

sdl2-compat:
-----------

https://github.com/libsdl-org/sdl2-compat

"This code is a compatibility layer; it provides a binary and source
compatible API for programs written against SDL2, but it uses SDL3 behind the
scenes."

https://github.com/libsdl-org/sdl2-compat/releases

SDL 1.2 and a few older versions of SDL 2.0:
-------------------------------------------

https://sourceforge.net/projects/libsdl/

https://sourceforge.net/projects/libsdl/files/SDL/

sdl12-compat:
------------

https://github.com/libsdl-org/sdl12-compat

"This code is a compatibility layer; it provides a binary and source
compatible API for programs written against SDL 1.2, but it uses SDL 2.0
behind the scenes. If you are writing new code, please target SDL 3.0 directly
and do not use this layer."

https://github.com/libsdl-org/sdl12-compat/releases

Actually, if you want to support the highest number of hardware devices and
operating systems, SDL 1.2 is the best library to use. The program will
function with:

SDL 1.2

sdl12-compat and SDL 2.0

sdl12-compat, sdl2-compat and SDL 3.0

So if you don't need the additional features of SDL 2.0 or SDL 3.0, your
program written for SDL 1.2 will have the highest support. The program will
compile in the same way regardless whether you use SDL 1.2 or sdl12-compat.

As shown below, some new GNU/Linux distributions are providing the
compatibility programs instead of the initial libraries. The addresses or the
next 2 pages are also available at https://web.archive.org/:

https://fedoraproject.org/wiki/Changes/SDL12onSDL2 (about Fedora 35)

"SDL 1.2 development ended long ago, with SDL 2.0 replacing it. However, many
older games still use SDL 1.2 and cannot change to SDL 2.0. In order to help
move SDL 1.2 games into the modern world, let's replace SDL 1.2 with
sdl12-compat, which uses SDL 2.0."

https://discussion.fedoraproject.org/t/f42-change-proposal-replace-sdl-2-with-sdl2-compat-using-sdl-3-self-contained/138987

"SDL 2 feature development ended some time ago with efforts being focused on
SDL 3. However, many older games still use SDL 2 and cannot change to SDL 3.
In order to continue to support SDL 2 games in the modern world, let’s replace
SDL 2 with sdl2-compat, which uses SDL 3. This also has the effect of moving
SDL 1.2 games to SDL3 through sdl12-compat running on sdl2-compat."
