The most obvious sign that Liverpool have already won the title is that bookmakers are not accepting bets on it.
As for next season, it will be a different team - Arnold will leave, Salah may leave, Van Dijk too, etc. It's too early to talk about next season as we don't know what kind of team Slot can put together plus we don't know what the competitors can do.
It would be very surprising if bookmakers still opened a bet for Liverpool to get the title at the moment. It would be like 1.02 or so I guess.

Extraordinary work they have done in the league so far.
TAA, Salah and van Dijk all are probable to leave but nothing is certain yet. Contract talks are ongoing. I hope Salah stays at least. TAA would probably sign for Real Madrid and I think van Dijk will leave for a Saudi team. Julian Alvarez's name is in the rumours but I don't know if Atletico Madrid would let him go easily. He is a superb finisher and I can't imagine what he can do in case of replacing this trash Nunez.