It's all fine. You can now find your cert under "User certificates".

Now set up the proxyserver and port in the wifi connection settings and browse a site like stackoverflow.com or github.com with a browser. You should see the decrypted traffic; delete the certicate and you'll be no longer able to see the decrypted traffic.

btw, having a User certificate installed usually doesnt help with apps, esp. when they come from big players like facebook, google, TikTok, etc.

Then you'd need to install a root certificate (yep, you ll need a rooted phone) and/or start using tools like frida.re, that actively can break into apptraffic that are secured with certificate pinning (means, the app doesnt accept any user or root certificate except their own).

KernelSU is pretty cool if you wanna dive into rooting...