[1.20.1] Shaders alpha channel don't work

At the time of forge 1.16.5, I used this code:

RenderSystem.enableBlend();
RenderSystem.disableAlphaTest();
RenderSystem.defaultBlendFunc();
// render
RenderSystem.disableBlend();
RenderSystem.enableAlphaTest();

But when switching to version 1.20.1, I ran into a problem: GL_ALPHA_TEST cap can no longer be enabled, and if you specify any color with alpha less than 1.0 in the shader, then the pixel color will still be with alpha 1.0

My current code:

Shader:

#version 330 core

out vec4 fragColor;

void main() {
    fragColor = vec4(1.0, 0.0, 0.0, 0.5);
}

@SubscribeEvent
        public static void registerShader(RegisterShadersEvent event) {
            try {
                event.registerShader(new ShaderInstance(event.getResourceProvider(), new ResourceLocation("untitled", "tst"), DefaultVertexFormat.POSITION), instance -> {
                    shaderInstance = instance;
                });
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

@SubscribeEvent
    public void render2D(RenderGuiOverlayEvent.Post event) {
        RenderSystem.enableBlend();
        RenderSystem.defaultBlendFunc();

        RenderSystem.setShader(() -> shaderInstance);

        Tesselator tesselator = Tesselator.getInstance();
        BufferBuilder bufferBuilder = tesselator.getBuilder();
        bufferBuilder.begin(VertexFormat.Mode.QUADS, DefaultVertexFormat.POSITION);
        bufferBuilder.vertex(0, 0, 0).endVertex();
        bufferBuilder.vertex(0, 50, 0).endVertex();
        bufferBuilder.vertex(100, 50, 0).endVertex();
        bufferBuilder.vertex(100, 0, 0).endVertex();
        tesselator.end();

        RenderSystem.disableBlend();
    }

If anything, the shader itself is working. I also tried rendering using POSITION_TEX vertex format, but nothing has changed.