certificate validation fails for trusted self-signed server certificate

I have encountered a scenario with unexpected behavior when trying to 
connect an SSL client (custom client application) to a server that is 
configured with a self-signed server certificate (it's not marked as CA, 
it's a leaf certificate) - more specifically, the server I'm testing 
against is:
https://self-signed.badssl.com/

I've configured the client by loading the server's certificate in an 
X509_STORE and then set that store on the SSL_CTX and I've set the verify 
mode to SSL_VERIFY_PEER.

The error I'm getting is X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT (error code 
18: "self-signed certificate").
The documentation for this error suggests even more that this should not 
happen, since the certificate was loaded into the store:
https://github.com/openssl/openssl/blob/openssl-3.5/doc/man3/X509_STORE_CTX_get_error.pod?plain=1#L193
"The passed certificate is self-signed and the same certificate cannot be 
found
in the list of trusted certificates."

The introductory documentation doesn't seem to cover this scenario:
https://docs.openssl.org/master/man7/ossl-guide-tls-introduction/#trusted-certificate-store

The OpenSSL version I've tested with is 3.5.0.

Is there something I'm missing? Some other configuration option? Or is this 
the expected behavior?

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