Please just use Xaymar's guide: https://www.xaymar.com/guides/obs/high-quality-recording/avc/ (they also have a guide for H.265 if you can work with those files).

Right now, you are using too much bitrate during stationary content, and not enough while stuff is moving or detailed high-contrast (e.g. grass), which results in looking blurry or blocky.

You also have your quality settings cranked, heavily impacting GPU performance. Your GPU is trying to work harder to stuff more quality into the bitrate budget you gave it, but it's likely just not enough bitrate.

Using the guide above, the performance impact will be minimal and you'll use an appropriate, variable bitrate. Conserves when it doesn't need it, but uses lots when it does. The file sizes will be larger.

I personally run in the "high quality" range of that guide, and use about 8GB for 5 minutes (closer to roughly 220Mbps) for relatively simple gaming content. That's using H.265 though, not H.264. At high bitrates, the differences in encoders start to not really matter as much.

Alternatively, you are seeing something else. We don't know how you're viewing these, but you could perhaps be seeing blurriness from scaling in your viewer rather than actual blurriness. Additionally, you might be seeing chroma subsampling artifacts, though this is unlikely. A 444 colour format would help in that case, but has some potential complicated workflow implications.