In my opinion effects like motion blur and depth of field make this game look way too blurry. As there are no in game options to adjust these other then general Post Processing setting, we have to make changes in game's config file.

Config file is located in below folder, you can just paste this link in your Windows Search as shown below.

%USERPROFILE%\Documents\My Games\GRID Legends\hardwaresettings\


Once there you need to open hardware_settings_config with Notepad or similiar text editor.
Inside the file you can find multiple post processing options described below:

motionBlur="true"
Self explanatory, just change "true" to "false" to disable blurring effect in motion.

depthOfField="true"
Its the effect of blurring things in the background, out of focus, change "true" to "false" to disable.

lensFlare="true"
This one affects the flare effect of light sources, like car headlights. Change to "false" to disable.

bloom="true"
This affects the glow or halo effect around lights, change to "false" to disable

Once you modify these to your liking you need to save changes and set file to Read Only by right clicking on the file hardware_settings_config and selecting Properties.

Disabling these effects will make GRID Legends look much sharper and more realistic. You might even get some performance improvement out of it. I recommend experimenting with these settings to find the combination that works best for you. Personally I recommend disabling at least motion blur and depth of field, as these are detrimental to game's visual quality.
Its difficult to showcase these effect on still pictures as differences are best visible in motion, but below you can see the picture with all these effects disabled. For me picture is sharper and without blindingly glowing lights.