The blurriness is caused by Bilinear filtering when down-scaling resolution. It can also be caused by running games in a higher resolution and setting your canvas & output resolutions to a lower resolution than what you are gaming at.
You have some encoding (Minor) You need to lower the load on your CPU.
If you don't cap your fps at all, try limiting it to 240fps as that is the frame rate you are wanting to record at.
- If you do cap your fps already, you need to lower it some more as your CPU just can't handle the workload of running at such a high rate whilst doing the recording at the same time (Even though almost all of the load is on your GPU as you use h264 - NVENC encoder, your CPU is still used)
You also have some very minor rendering lag, I am pretty sure this will clear up by itself if you manage to remove the encoding lag, as it is only 0.4% of the frames rendered that are lagged.
Once you get your encoding lag under control, you could try using High Quality preset, High profile and Lanczos downscale filtering. This will put a little more load on the NVENC encoder, though your GPU should most certainly handle it, even at 240fps.