According to a translation by the Arc System Works social account, this delay is to allow the team to implement rollback netcode. The release date will now be shared at a "later time", so when we get an update, we'll let you know. Here's the full message:
The release timing for HUNTER×HUNTER NEN×IMPACT will be changed from the previously announced 2024 timing to now release within 2025.
We sincerely apologize for the trouble caused by this delay to the players who are looking forward to the game's release.
This delay is so that we will be able to implement rollback netcode for release. *Rollback netcode is a system that reduces the feeling of connection delay when playing online matches.
We made this decision out of concern that players would not be able to fully enjoy the game in a state where some players would encounter issues with online play, given the nature of fighting games.
The release date will be announced at a later time. We appreciate your understanding, as we continue to work to provide the best game possible.
From the HUNTER×HUNTER NEN×IMPACT Production Team
Hunter x Hunter: Nen x Impact was originally revealed earlier this year in January and confirmed for the Switch in March.