I already fixed the textures that were broken. Now the cars are visible, and the heads that were missing are also showing (although they have a black texture. I need to check what happened there). The game no longer crashes, and I was able to complete a couple of missions without any issues

vendor/librw/src/gles1/gl1matfx.cpp

@@ -0,0 +1,86 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#include "../rwbase.h"
+#include "../rwplg.h"
+#include "../rwpipeline.h"
+#include "../rwobjects.h"
+#include "../rwengine.h"
+#include "../rwrender.h"
+#include "../rwanim.h"
+#include "../rwplugins.h"
+#include "rwgles1.h"
+#include "rwgles1plg.h"
+#include "rwgles1impl.h"
+
+#ifdef RW_GLES1
+
+namespace rw {
+namespace gles1 {
+
+void
+matfxRenderCB(Atomic *atomic, InstanceDataHeader *header)
+{
+    uint32 flags = atomic->geometry->flags;
+    setWorldMatrix(atomic->getFrame()->getLTM());
+    glDisable(GL_LIGHTING);
+
+    setupVertexInput(header);
+
+    InstanceData *inst = header->inst;
+    int32 n = header->numMeshes;
+
+    while(n--){
+        MatFX *matfx = MatFX::get(inst->material);
+        Material *m = inst->material;
+
+        // En GLES1 sin shaders: ignoramos env map, solo dibujamos textura base
+        setMaterial(flags, m->color, m->surfaceProps);
+        setTexture(0, m->texture);
+        rw::SetRenderState(VERTEXALPHA, inst->vertexAlpha || m->color.alpha != 0xFF);
+        drawInst(header, inst);
+        inst++;
+    }
+
+    teardownVertexInput(header);
+}
+
+ObjPipeline*
+makeMatFXPipeline(void)
+{
+    ObjPipeline *pipe = ObjPipeline::create();
+    pipe->instanceCB   = defaultInstanceCB;
+    pipe->uninstanceCB = defaultUninstanceCB;
+    pipe->renderCB     = matfxRenderCB;
+    pipe->pluginID     = ID_MATFX;
+    pipe->pluginData   = 0;
+    return pipe;
+}
+
+static void*
+matfxOpen(void *o, int32, int32)
+{
+    matFXGlobals.pipelines[PLATFORM_GLES1] = makeMatFXPipeline();
+    return o;
+}
+
+static void*
+matfxClose(void *o, int32, int32)
+{
+    ((ObjPipeline*)matFXGlobals.pipelines[PLATFORM_GLES1])->destroy();
+    matFXGlobals.pipelines[PLATFORM_GLES1] = nil;
+    return o;
+}
+
+void
+initMatFX(void)
+{
+    Driver::registerPlugin(PLATFORM_GLES1, 0, ID_MATFX, matfxOpen, matfxClose);
+}
+
+}
+}
+
+#endif