1. Add the Salesforce My Domain URL in your Remote Site Settings in Setup in the Source org.

Remote Site Setting:

2. Create a Connected app in the target org. Make a note of the Consumer Key and Secret.

Sample Code:

HttpResponse response = new HttpResponse();
HttpRequest req = new HttpRequest();
Http objHttp = new Http();
String strEndPoint = '{YOUR_DOMAIN_URL}';
String strUsername = '{YOUR_USERNAME}';
String strPassword = '{YOUR_PASSWORD}';
String strClientId = '{YOUR_CONNECTED_APP_CONSUMER_KEY}';
String strClientSecret = '{YOUR_CONNECTED_APP_CONSUMER_SECRET}'; 
String strBody = 'username=' + strUsername;
strBody += '&password=' + strPassword;
strBody += '&client_id=' + strClientId;
strBody += '&client_secret=' + strClientSecret;
strBody += '&grant_type=password';
req.setHeader( 'Content-Type', 'application/x-www-form-urlencoded' );
req.setBody( strBody );
req.setEndpoint(
    strEndPoint + '/services/oauth2/token'
);
req.setMethod( 'POST');
response = objHttp.send( req );
System.debug(
    'Access Token Response is ' + response
);
if ( response.getStatusCode() == 200 ) {            
        
    Map < String, Object > resultMap = ( Map< String, Object> )JSON.deserializeUntyped( response.getBody() );
    String strAccessToken = ( String )resultMap.get( 'access_token' );
    
    System.debug(
        'Access Token is ' + strAccessToken
    );
        
    req = new HttpRequest();
    req.setHeader( 
		'Content-Type', 'application/json' 
	);
    req.setHeader( 
		'Authorization', 
		'Bearer ' + strAccessToken 
	);
    req.setEndpoint(
        strEndPoint +
        '/services/data/v57.0/sobjects/Account/'
    );
	strBody = '{ "Name" : "Testing", "Description" : "Testing" }';
	req.setBody( strBody );
    req.setMethod( 'POST' );
    response = objHttp.send( req );
    System.debug(
        'Create Account Response is ' + response
    );
    
    if ( response.getStatusCode() == 200 ) {            
    
        System.debug(
            'Response Body is ' + response.getBody()
        );
    
    }
    
}

Output: