The quickest wins are built right into the mod list. MGO’s STEP 3 folder offers a few presets. These default to the performance options, but if you’ve switched to quality and find that your machine is struggling, it’s worth considering switching back. The performance presets still look great, and they’re significantly easier on your hardware.
Community Shaders has a Performance preset (the default) and a Quality preset. Quality looks better outdoors, but it will cost you some frames.
Grass Density and LOD Distance have optional Quality presets too. Leave them unchecked to stay on the lighter settings.
See Onboarding for where to find these in MO2. If you’re short on frames, this is the first place to look.