Unfortunately, it’s possible that Just Cause 5 was already cancelled.

Square Enix officially announced they were working on a new game in the Just Cause franchise in their financial report last 2022. They didn’t officially reveal that this was Just Cause 5, but it’s the common perception that that was the case.
As reported by MP1st, a developer working at Sumo Digital indicated in their LinkedIn profile that they worked as Vehicles Feature Team Lead for Just Cause 5 from July 2021 to July 2023. This is the first time someone in the industry confirmed that the game in development is Just Cause 5.
Now, it’s possible that all this profile confirms is that Sumo Digital was working on the game for two years. Square Enix may just as likely have moved development of the project to another studio. If we’re fortunate, they may have opted to bring the project back to the studio that’s made all the games in the franchise until now, Avalanche Studios.
We do know that Avalanche Studios is currently preoccupied with making Xbox exclusive co-op heist game, Contraband. Word about that project was not entirely positive, but we also haven’t heard much about it for a few months now. So there’s no frame of reference if it’s at a much better place or not. For all we know, Microsoft already has plans to stealth drop it within this financial year.
Regardless of where Avalanche Studios is, Square Enix is itself in a perilous position. Two years after announcing Just Cause 5, Square Enix announced plans to lower their video game output and reorganize the whole company. This year, they revealed that they are now under a three year timetable for a complete reboot of the company.
That reboot specifically claims that they intend to shift development of their games away from outsourcing back to their internal studios. This would give us good reason to believe that Square Enix has decided to drop Just Cause 5.
The Just Cause franchise didn’t become popular for a particularly solid narrative, but instead for having enjoyable open worlds, that encouraged players to go over the top and just indulge in action movie escapist fantasy. So the stakes for these games aren’t as high compared to, say, Final Fantasy or Kingdom Hearts, and expectations aren’t that high. On the flip side, it’s also not expected to be as profitable as Square Enix’s key franchises, so it wouldn’t be a huge priority. It’s possible that Just Cause 5 wasn’t quite cancelled, but Square Enix could have chosen to pause work on it for now. We don’t expect Square Enix to make an official announcement for this, but we’re sure fans would want to be told so they don’t have to keep wondering.