Pentium D processors are pretty power hungry, so factor that into your thoughts. Also make sure you put a modern OS on it that is getting security updates. It probably has Win XP or Vista installed which isn’t safe to connect to any network.
It should work fine as a router as long as you don’t enable any of the packet inspection features. For basic routing and firewalling for a home network it should be plenty powerful. I would personally put a small SATA SSD in it as the main drive and ditch the 90GB HDD.
As an additional idea, if you put a larger SATA drive or two into it you could make it a NAS.
Ryzen laptops which feature capable integrated GPUs serve light and medium gaming tasks well. For heavy use, there are desktops, which is where the real power is. Portable systems like the Steam Deck are also hitting from the mobile side as well.
Gaming laptops have always been an extremely niche product and have gotten squeezed from all ends in recent years.