For some reason, UE 5.0 and newer default to sub 100% resolution. Most likely due to the fact that TSR is expected to upscale the image to 100% resolution, so it defaults to performance savings.
The Screen Percentage value won’t be 100 for most of the new projects. Once you set it to 100, you can then try to switch back to Temporal AA from TSR. TSR is better overall, but handles this kind of scenario arguably worse than TAA:
After these two changes, the last possibility is that the opacity maps of the grass materials could have their texture filtering/mip mapping disabled, which some people do for some reasons.