If you want to learn more about the double ratchet algorithm, this explanatory video is excellent.

https://youtu.be/7uEeE3TUqmU?si=Sf9ekYhGi2xWFFBV nostr:note1ffgsgvkltl96wzwe6lakv2ntjfkq2u48msx57mrvnnhtyde5s2js8antlr