As you correctly identified, there are two types of seed nodes, i.e. DNS seeds and seed nodes. DNS seeds are stored in chainparams.cpp. As of today (September 2021) the following nodes are listed in this file.
I performed nslookups on these DNS names and they return a list of IP addresses that all seemed to be running bitcoin nodes.
There is also the concept of seed nodes which are hardcoded IP addresses in the event that someone is experiencing a DNS failure or other issue. These nodes are only contacted if no other discovery mechanism works.
You can also use
-seednode option to connect to a node (IP address) to retrieve peer addresses, then disconnect.