Hi, do you know how to solve this problem?

I was playing fine on my PS4 Slim until a few weeks ago. I noticed my loading speed dropped drastically; it's normally around 300 Mbps. I searched on Google for a solution and have tried practically everything. I've changed the DNS settings and other things on my router, they even replaced the router, and they cleaned and replaced the thermal paste on my PS4. I don't know what else to do to fix the problem. Does anyone know how to solve it?