EGL is used at minimum in 3 places (beside the GLES context creation):

1. At init, to create a small pbuffer to get Hardware information support. This part can be skipped with LIBGL_NOTEST=1

2. For eglGetProcAddress to get extension function adresses.

3. for eglSwapBuffers to swap buffers (actually put drawing onscreen).

It should be working for you now.
Some gidelines:

Compile with NOEGL (the NOX11 will be set anyway).
Use with Export LIBGL_ES=2 (or define a DEFAULT_ES=2 at compile time).
You will need to create the GLES context yourself
There is no Hardware checking for capability, so only basic functions will be used
You need to SwapBuffers yourself. To stay on the safe side (because gl4es has many optimisations and may cache/batch drawing calls), it's better to call either glFlush() or glFinish() before the SwapBuffers.

For dlopen/dlsym.
dlopen open an handle, and "load" a dynamic library. Then, with dlsym, you get address of a function based on it's name.
gl4es works like this: for example, if your program use glDrawElements(...)
Because you are linked (staticaly or dynamcaly) to gl4es, you call the glDrawElements(...) from gl4es, that is an alias for gl4es_glDrawElements(...)
This fonction will do some specific stuff, depending on the parameters used (for example, you can call with GL_QUADS that is not supported on OGLES2, but is supported on full OpenGL, and gl4es will handle that as well).
At some point, gl4es will call the "real" glDrawElements(...) from OGLES2 driver, so it will get the function pointer using dlsym(gles, "glDrawElements") and call that function, so the GLES2 driver can draw the things.
All call in gl4es are wrapped in a similar way. You never call function from the GLES2 driver directly. It gl4es that does it. And gl4es will make some optimisation, cache things, and limits the number of calls to GLES2 driver to try get more speed...

I'm not confident this will work. You will have name collision between the ogles2 function name and gl4es funciton name, that will be the same. That's why I use dlopen on gl4es. the glXXX name of gl4es are the one to be used by the program, and the glXXX name of ogles2 are the one used only by gl4es. But those are the same name, so if you link with both ogles2 and gl4es, how to know wich one to use? Or maybe I haven't understood how that OpenLib works...

I must insist, gl4es is not working like Regal. Regal create some new function, with a different name, where gl4es create full OpenGL functions. I have not created any "mangling" mecanism for gl4es. gl4es is an OpenGL library: you put it in your system and you use OpenGL program without recompiling.

Now, can I just use that AmigaGetGLESProc(...) function from SDL? will it give the ogles2 function pointer without masking the gl4es function?

ram:> a.out
LIBGL: Initialising gl4es
LIBGL: v1.0.5 build on Feb 17 2018 12:36:08
LIBGL: Using GLES 2.0 backed
LIBGL: Hardware test disabld, nothing activated...
LIBGL: warning, gles_glGetIntegerv is NULL

21483 frames drawn, for a total of 8169.000000 milliseconds
Took approximately 0.380254 milliseconds per frame
Avarage FPS: 2629.820051
Took approximately 0.474701 milliseconds per frame (with swap)
Avarage FPS (with swap): 2106.589527

27488 frames drawn, for a total of 10097.000000 milliseconds
Took approximately 0.367324 milliseconds per frame
Avarage FPS: 2722.392790
Took approximately 0.470714 milliseconds per frame (with swap)
Avarage FPS (with swap): 2124.430018

32814 frames drawn, for a total of 16080.000000 milliseconds
Took approximately 0.490035 milliseconds per frame
Avarage FPS: 2040.671642
Took approximately 0.587737 milliseconds per frame (with swap)
Avarage FPS (with swap): 1701.441460

LIBGL: Initialising gl4es
LIBGL: v1.0.5 built on Feb 17 2018 23:41:49
LIBGL: Using GLES 2.0 backend
LIBGL: OGLES2 Library and Interface open successfuly
LIBGL: Hardware test disabled, nothing activated...
LIBGL: Targeting OpenGL 2.0
LIBGL: Current folder is:RAM Disk:
20457 frames drawn, for a total of 11217.000000 milliseconds
Took approximately 0.548321 milliseconds per frame
Avarage FPS: 1823.749666
Took approximately 0.652686 milliseconds per frame (with swap)
Avarage FPS (with swap): 1532.130018

MiniGL: 0.488850
gl4es: 0.548321
MGLReloaded: 0.571977
Regal: 1.109902

So, once i try to run it as it, it freeze amigaos. But not all the time on the same place.

glFlush();
IOGLES2->aglSwapBuffers();
glDrawBuffer(GL_BACK);
display();
glDrawBuffer(GL_FRONT);

display();
IOGLES2->aglSwapBuffers();

As for crash: sure, gl-code-wise it can be wrong, but it works copy of minigl example,

And you know what trashed data for a normal likely is? Most likely not a normal anymore And a normal which is not a normal may easily provoke crashs on code which asumes that it is a normal.

Please fix the normal-array and try again.