It seems you didn't understand what was explained in this thread. As soon as there is any kind of scaling, especially upscaling, a certain amount of blurriness is always involved.This is the nature of scaling. The smaller the difference between original resolution and output resolution, and the smaller the original resolution, the more prominent are the scaling artifacts.
For example, if you set your game to 1280x720 and play and record with this resolution, your videos will become crystal clear for anyone who will watch your video in this resolution. But you will not see this, because your monitor is 1366x768, which is slightly higher, so your monitor will upscale and make your image blurry. This blurriness is only visible by you, it is not in the video you record.
If you watch any 1080p video, it is 1920x1080. This is always downscaled to 1366x768 for you, or even lower, if you don't watch fullscreen. Downscaling doesn't make a video as blurry as upscaling, so a 1080p video may appear crystal clear to you.
The only thing to remedy all this is to produce the original source in a resolution that is kept by Youtube. These are 1440p, 1080p, 720p. To get a clear downscaled video from Youtube, you need to have a 1080p video uploaded to Youtube, and this 1080p must not be an upscaled 1366x768 video but must be created as 1920x1080p by the game with an OBS canvas and output size of 1920x1080 in the first place. That means your game must run at 1920x1080, and this is probably only possible if you use a monitor that supports this resolution.
It may be possible to create this as virtual resolution if you use the DSR feature of your Nvidia card. But with DSR, it again might appear to you that your image becomes blurry, because you get a 1920x1080->1366x768 downscaled view of everything. Try DSR, if it is offered in Nvidia control panel. However, it may be that your CPU isn't fast enough to support your game running in that resolution - it's double the pixels, thus double the system requirements.
It's all about scaling, and with a 1366x768 display there is always some kind of scaling and blurriness involved. There is a reason, why Smartphones with their tiny displays get HD (1080p), WQHD (1440p) and UHD (2160p) resolutions.