Check obj a and obj b fields have same values

// Replace ObjA__c and ObjB__c with your actual API names if different
List<ObjB__c> objBList = [
    SELECT Id, abc__c, xyz__c, ObjA__r.Id, ObjA__r.abc__c, ObjA__r.xyz__c
    FROM ObjB__c
    WHERE ObjA__c != null
];

for (ObjB__c b : objBList) {
    if (b.ObjA__r != null) {
        Boolean isAbcSame = (b.abc__c == b.ObjA__r.abc__c);
        Boolean isXyzSame = (b.xyz__c == b.ObjA__r.xyz__c);
        
        System.debug('ObjB Id: ' + b.Id);
        System.debug('abc__c same? ' + isAbcSame);
        System.debug('xyz__c same? ' + isXyzSame);
        
        if (!isAbcSame || !isXyzSame) {
            System.debug('Fields do not match for ObjB Id: ' + b.Id);
        }
    }
}