Salesforce won't let you select star (SELECT *). This is a workaround where you generate the SOQL manually by inspecting the schema of the table.

select_star_in_salesforce_apex.cls

Map<String, Schema.SObjectField> field_objmap = schema.SObjectType.Opportunity.fields.getMap();
List<Schema.SObjectField> field_objmap_values = field_objmap.values();
List<String> field_names_list = new List<String>();

for(Schema.SObjectField s : field_objmap_values) {
    String field_label = String.valueOf(s.getDescribe().getLabel()); // Perhaps store this in another map
    String field_name = String.valueOf(s.getDescribe().getName());
    String field_type = String.valueOf(s.getDescribe().getType());
    
    field_names_list.add(field_name);
}

String q = 'SELECT ';
q += String.join(field_names_list, ',');
q += ' FROM Opportunity WHERE Name = \'foobar\'';

// print the query
System.debug(q);

Opportunity opp = Database.query(q);

// confirm it worked
System.debug(opp.Name);