That domain does not use Cloudflare. You can see the nameservers in the whois are not set to Cloudflare. DNS queries do not return Cloudflare proxy IPs either.
Domain Name: THEHIGHLANDSUN.COM
...
Updated Date: 2023-09-23T06:07:37Z
Creation Date: 2015-09-12T20:27:26Z
Registry Expiry Date: 2024-09-12T20:27:26Z
Registrar: Internet Domain Service BS Corp
Registrar IANA ID: 2487
...
Name Server: NS48.WPXHOSTING.COM
Name Server: NS49.WPXHOSTING.COM
DNSSEC: unsigned
...
>>> Last update of whois database: 2023-10-02T05:33:39Z <<<
There is reference to m88xin.com in the Cloudflare 521 error displayed in your site. Do you have some embed from that domain in your site’s header?