Before anything else, make sure to check what apps are taking up the GPU in the Task Manager,
back in late 2018 just before my first dedicated GPU arrived, I was lagging, I checked my Task Manager and what would ya' know it, some fella' infected my system with a Bitcoin Miner,
There is an option in the Task Manager to view the GPU usage (I'm referring to the one in the first tab, not the PERFORMANCE tab), look at what takes up that GPU usage and report back if you find anything interesting.