According to the latest manga chapter of Kaguya-sama: Love is War, the story will be headed towards its ending from the next one. Yes, every manga is technically headed towards its ending from the very first chapter. However, what this means is that the author is teasing it himself, and he should know how close it is. According to the chapter, Akasaka Aka wrote: “From now on the story enters the final phase”. The cover of the latest volume features Shirogane by himself:
The author already teased something similar on Twitter back in August. He said that it went for longer than he imagined and that the midfield game was over. He also said that it had entered the ‘final game’ and asked the fans to stick around for a while longer.
Note that midgame being over most likely meant that the story entering the ‘final game’ meant the last third (so 2/3 over). It’s not to be mixed with a ‘final arc’ and the manga wasn’t likely to end very soon. Still, it has been over 3 months since then, so it’s bound to get closer to the ending. My guess is that there may be a few more arcs (or one long one) left, but don’t take that as facts or any sort of indicator.
Kaguya-sama manga has been serialized since 2015, and fans are not really ready to see it ending yet. Especially considering it’s 2020 and that the year has already marked with many sad news already. Although there’s also good news, as the anime will be getting both an OVA and Season 3 soon!