hi agdg, this is the scene node's script that is setting stuff on a sprite2d:

extends Node2D
var bg_seed_timer = 0
const bg_seed_change_duration = 2.0
var bg_next_texture
var bg
func _ready():
	bg = get_node("background")
	bg_next_texture = bg.texture.duplicate()
	bg_next_texture.noise = FastNoiseLite.new()
	bg_next_texture.noise.seed = randi()
	bg.material.set_shader_parameter("next_texture",bg_next_texture)
	#bg.material.set_shader_parameter("starttime",fmod(Time.get_unix_time_from_system(),3600))
	return
func _physics_process(delta):
	bg_seed_timer += delta
	if bg_seed_timer >= bg_seed_change_duration:
		bg_seed_timer -= bg_seed_change_duration
		bg.texture.noise.seed = bg_next_texture.noise.seed
		bg_next_texture.noise.seed = randi()
		#await bg_next_texture.changed
		#await bg.texture.changed
	bg.material.set_shader_parameter("timebump",bg_seed_timer/bg_seed_change_duration)
	return

and this is the shader for that sprite (trimmed some stuff that's not running during tests):
shader_type canvas_item;
uniform float starttime;
uniform sampler2D next_texture;
uniform float timebump;
void fragment() {
	vec2 uv = UV;
	COLOR = mix(texture(TEXTURE,uv),texture(next_texture,uv),timebump);
}

i am passing a float "timebump" on every frame instead of passing the initial time to the shader for testing purposes, i know it can be frowned at...