If you want to check for duplicates before trying to insert, that too can be done using the FindDuplicates class in Datacloud namespace.

Find existence of duplicates before insertion

Class__c classToCreate = new Class__c(Name='Science', Grade__c=8);
List<Class__c> duplicates = findDuplicateRecords(classToCreate);
if(duplicates.size() == 0){
    //no duplicates
    insert classToCreate;
} else{
    //desired update
}


public static List<SObject> findDuplicateRecords(Class__c classToCreate){
 List<Class__c> classList = new List<Class__c>();
    classList.add(classToCreate);
        
    List<Datacloud.FindDuplicatesResult > findDuplicatesResult = Datacloud.FindDuplicates.findDuplicates(classList);
        
    Datacloud.DuplicateResult duplicateResult = findDuplicatesResult.get(0).getDuplicateResults().get(0);
    Datacloud.MatchResult matchResult = duplicateResult.getMatchResults()[0];
    List<Datacloud.MatchRecord> matchRecords = matchResult.getMatchRecords();
    
    List<SObject> duplicates = new List<SObject>();
    for(Datacloud.MatchRecord matchRecord : matchRecords){
        SObject duplicate = matchRecord.getRecord();
        System.debug('Match Record: ' + duplicate);
        duplicates.add(duplicate);
    }
    return duplicates;
}