So about the Owl House thing*TM. Duolingo has always been more "open" about queer people mostly out of practicality. It covers more bases and saves on programming random phrases to not be concerned about gendered taboos. As such, some of the "stories" it tells end up being queer oriented. Around the time these characters were introduced, the Owl House had been running for a while, with comparisons between the titular owls being received positively by both companies.
Then Amity and Luz started dating.
People obviously were hyped, but this connection brought attention to two of the new characters in Duolingo, Lily and Zari, who obviously share more than passing resemblance to Luz and Amity, even in personality. As such, Duolingo users started pairing the two. This lead to Duolingo listing the Owl House as one of Lily's interests, and advertisement featuring the pair together being more common.