Well, muru is correct in [their comment](https://askubuntu.com/questions/1376524/how-does-sources-list-of-21-10-impish-indri-look-like#comment2370426_1376524). Also the [highest-voted answer](https://askubuntu.com/a/192388/618353) in the dupe says this:
If you're using another release, you need to replace the precise word with your Ubuntu release name. You can see which name you should use with this command:
lsb_release -c -s