CK3 dynasty IDs
10,398 dynasties in Crusader Kings III 1.20.0.3, read from common/dynasties, and 604 cadet houses written into the files (common/dynasty_houses). The ID is the one the game's files use: a history character says dynasty = 812, scripts say dynasty:812.
The console's dynasty_prestige [amount] [dynasty id] adds renown; without an ID it uses your own dynasty, which needs no lookup.
Dynasties by name
Houses
All 604 scripted houses with the dynasty each belongs to.
Source: game/common/dynasties, game/common/dynasty_houses and the English localisation, Crusader Kings III 1.20.0.3. Commands as listed on the official wiki's console page. See also title IDs, character IDs, dynasty IDs and nicknames.