Whitelisted iframes - took too long to respond. any way to understand where the problem is

Support
1

The iframe domain is properly whitelisted in /admin/site_settings/category/security?filter=iframe

the embedded page is very fast, properly configured ( X-Frame-Options: None Content-Security-Policy: None The URL allows iframing.)
and easily embedded as iframe in other sites,

Discourse showing the took too long grey box

Any ways to identify the problem? The chrome console shows no errors

The image displays a grey text error message that reads, "exponanta-public.s3-website-us-east-1.amazonaws.com took too long to respond." (Captioned by AI)
The image displays a grey text error message that reads, "exponanta-public.s3-website-us-east-1.amazonaws.com took too long to respond." (Captioned by AI)1076×500 12.8 KB