Problem with underwater shader on ColorRect

[jaroslaw.smiglak]

Godot Version

3.5

Question

Hello everyone. I’m new to the forum and hope someone can help me. I’m developing a 2D game where everything takes place underwater. I’m having problems with shaders.
I have attached a screenshot and the shader code. All that comes out is gritty pixel flickering. I just can’t get any further. Unfortunately I don’t know whether it might be due to the hardware. Maybe someone knows a solution.

Here the shadercode:

shader_type canvas_item;

uniform float wave_speed = 3.0; //wave loop speed
uniform float wave_freq = 10.0; //wave vertical freq
uniform float wave_width = 1; //wave width 
void fragment(){
	vec2 scale_UV = SCREEN_UV;
	vec2 wave_uv_offset;
	wave_uv_offset.x = cos((TIME*wave_speed)+UV.x+UV.y*wave_freq*2.0)*wave_width*0.01;
	//COLOR = vec4(wave_uv_offset,0.0,1.0);
	COLOR = texture(SCREEN_TEXTURE,scale_UV+wave_uv_offset);
}