Records owned by User

RecordsOwnedByUser.cls

Id userId = '005i000000XXXXX'; //Input userId

Map<String, Schema.SObjectType> sobjects = Schema.getGlobalDescribe();
system.debug('sobjects: ' + sobjects);

Map<Schema.SObjectType, Integer> ownerMap = new Map<Schema.SObjectType, Integer>();

for(Schema.SObjectType sobj : sobjects.values())
{
    Set<String> objectFields = sobj.getDescribe().fields.getMap().keySet();

    Boolean queryable = sobj.getDescribe().isQueryable();

    if(objectFields.contains('ownerid') && queryable) {

        Sobject[] results = Database.query('SELECT Id FROM '+sobj+' WHERE OwnerId = :userId Limit 1000');

        if(!results.isEmpty()){
            ownerMap.put(sobj, results.size());
        }
    }
}

for(Schema.SObjectType item : ownerMap.keySet()){
    system.debug(item+': ' + ownerMap.get(item));
}