Cloudflare couldn’t find the website’s server. Not you.
Cloudflare asked where the website’s server lives and got no usable answer. Waiting won’t change it. Configuration. Until the owner fixes it.
Nothing on your side causes this. VPN, cookies and browser do not matter here.
Check every DNS record in the zone resolves; fix dangling CNAMEs; confirm the domain is active on Cloudflare.
Cloudflare’s documentation