You'll always have Processes running - Windows cant function without background Processes. You can see these in the TaskManager on the Processes tab (not Applications tab). You can also check the Services tab and turn off things you know you dont need - but be careful there. Like processes, Windows needs some Services running to function properly and turning them off will crash or disable necessary services.
Have you updated Java lately? If you haven't, you may need to.
If you have a second hard drive, I'd recommend installing a fresh copy of Windows to that drive and not install any applications or utilities other than MC. Don't even install Win updates because a recent update could have changed a Process or Service that's causing it. If the same lag happens, it would point to a hardware issue like RAM, processor, GPU, network adapter or motherboard. Yes you have enough RAM on both the motherboard and GPU - but it's possible that a device is failing or acting up. A piece of RAM is failing and has bad sectors so when MC uses it, there's lag while it retries the operation on another sector. Or the video card is starting to fail and choking on certain graphic operations - like opening a chest and loading all the items/images.
Are you getting lag in any other games that worked fine before but now has hiccups here and there? Things similar in MC CPU/GPU usage like Cities Skylines or Stardew Valley - not high performance games like an FPS that rely on bandwidth or framerate. This won't prove software or hardware, but it will prove/disprove that it's just MC acting up.
