Poor Performance of Advance SSL Certificate

Hi, I’m using an Advance SSL certificate but the performance is really poor. When I was using the default Universal SSL certificate, the performance was acceptable but now after purchasing the advance certificate, the performance is worse.
The issue isn’t related to my server. Because before using Cloudflare, I was using the Let’s Encrypt certificate on my server and the performance was good enough.
Please help me improve the certificate performance.

I don’t understand how Advanced SSL certificate can impact a website performance. It’s just TLS encryption/decryption.

So, what tools you used to measure the performance? GTmetrix? web.dev?

I’m using that certificate on my API built with node.js.
I’m not actually using any of these tools you mentioned for performance measuring. Because the API response is clearly visible when I request something. One more reason I can’t use these tools is that the APIs are protected with token authentications.