The safe navigation operator still returns null if a null is in the path, so you have to check for that:

if(c?.Status__c?.Contains('Released') == true){ // get the Error on this line
        System.debug('Contains');
}

Or, in an even modern alternative, you can use the null-coalescing operator:

if(c?.Status__c?.contains('Released') ?? false) {
    System.debug('Contains');
}

The main point is that ?. can return null, but a condition always expects true or false. The null-coalescing operator can help in these situations.