The website’s certificate is invalid. Not you.
Cloudflare checked the website’s server certificate and rejected it — expired, wrong name, or not trusted. Waiting won’t change it. Only the owner can renew or replace the certificate.
Nothing on your side causes this. VPN, cookies and browser do not matter here.
Renew or replace the origin certificate, or install a Cloudflare Origin CA certificate. Full (strict) requires a certificate Cloudflare can validate.
Cloudflare’s documentation