The 60Hz TV isn't causing it, though running floating FPS numbers above 200 on a 60Hz display might cause enough judder for the game to feel laggy. If your game is running at 250fps and your monitor at 60, then you're rendering 4.167 frames per displayed frame, meaning that every ~5 displayed frames your main visible rendered frame will shift 1 frame "forward" compared to the cadence of the previous frames, which while you might not notice visible tearing, will make for visibly uneven motion. If the framerate fluctuates (which it does unless it's locked down) this variance will be bigger, more pronounced, less consistent, and more annoying. It's the kind of thing that is very often not consciously perceptible, but very much unconsciously so. Enabling some form of VSYNC (or better, enhanced sync alongside a framerate lock to a number your GPU can maintain constantly and that is an integer of your monitor's refresh rate) will allow you to check if this is the case. If unlocked, non-synced twohundredandwhatever fps feels laggy, but (driver/software) synced and constant 180fps doesn't, then your "lag" issue is frame pacing judder, not lag. If there's no perceptible difference, then judder is not your problem, and you can more or less exclude a new monitor fixing this (though a faster monitor will definitely be a better experience overall).
Did installing Malwarebytes actually deactivate Windows Defender though? It shouldn't be running at all if Windows recognizes another AV program installed.
