This method is almost always mentioned in the lists of free Telegram channel about stbemu codes promotion methods. But you yourself understand that potential readers rarely look for new channels in catalogs.
Registration in directories is necessary so that the authors of other channels can find your channel for mutual PR. And later – potential advertisers who are looking for platforms to advertise their product.
Directories where you can register for free: Tgstat, Telegros, Tlgrm.