Googlebot with name "Chrome Privacy Preserving Prefetch Proxy" tries to find instructions if it can preload your website for the user surfing on Chrome (Chrome thinks, for example, the link to your website is going to be clicked on).
Basically what we, webmasters, are interested in is to get rid of 404s caused by this feature. The most simplest way is to create the file traffic-advice (without any extension) in the directory .well-known with the content:
[{
"user_agent": "prefetch-proxy",
"google_prefetch_proxy_eap": {
"fraction": 1.0
}
}]
The bot requires a specific MIME type. On Apache, you can add these lines to the main .htaccess file:
# vi .htaccess RewriteRule ^\.well-known/traffic-advice$ - [T=application/trafficadvice+json,END] <FilesMatch "traffic-advice"> Header set Content-Type "application/trafficadvice+json" </FilesMatch>