The game shipped 3 million its first week nearly two years ago, and since then sales have apparently nosedived, moving only another half a million since:

https://www.vgchartz.com/article/464167/final-fantasy-xvi-sales-top-35-million-units/

For context, the previous entry, FF15, sold 6 million in its first two months, and over 10 million as of 2022.

This is the market telling SE that they don't want a Action game from them.
They have to go back to having more RPG elements, and preferably dropping the action-lite rpg root as well.
Go back to turn base please SE.

Stop chasing new audiences! (at the cost of your old ones) 
Just give your fans what they want, and make each game better than the last, and things will slowly grow.
Also stop reinventing the wheel. If you want to grow a fan-base, there needs to be consistency with how the games look/feel/play.

It should be obvious, to most everyone.

I agree but honestly, they abandoned their old audience so long ago that I don't think they can even get them back at this point. I think Square-Enix needed to course correct a long time ago, but they just never did and I fear now it's probably too late.

And I say this as someone who actually enjoyed FF15 a lot. 

My girlfriend got this for me for Christmas, so in a way I'm responsible for one of those sales. I still haven't opened it but plan to whenever I hook up my PS5 again

I was a huge FF fan in the past, I even enjoyed FF13 very much. But I don't know, I watched a bunch of trailers and FF16 looked somewhat dull and boring. I have no urge whatsoever to get this game. Maybe when I see it on sale for 10 bucks or something. But even then I would have to think about it, lol.

I'll wait for the official figures, but it's safe to say it underperformed. The series isn't doing great, and even FF14 declined after an apparently crappy expansion.

What they should be doing is build on the FF7 Remake/Rebirth/Re-next forumla and apply it to the next mainline game, release it on as many platforms as possible, and hope for the best. Great games don't always sell gangbusters, and sometimes it's no one's fault that a game underperforms or a franchise declines/stagnates.

FF16 underperforming does have a few obvious reasons behind it. This thing isn't even a RPG, it's closer to a Devil May Cry light. I do think the "JRPG cap" is real, but if you're not too careful in retaining enough core elements of a beloved series, you might end up losing more players than gaining.

I feel like this number is some kind of misunderstanding or miscommunication. As far as I’m aware there is exactly one source for it, a Japanese video games analyst who said it was stated during an investor call.

The Steam sales are estimated by all sources to be in the region of 500k, with ranges from 430k - 645.5k. So for this number to be correct then the Steam numbers need to be on the low end of the estimate, Square would have shipped zero more physical copies since day one and it sold an almost negligible number of digital copies on PS5 in almost 2 years. This all seems a little much.

The alternative being the original 3m number was wrong, which seems unlikely.

Its not sustainable for the series to be exclusive to one platform especially considering how different each entry is.

FFVII did better due to its recognition and FFXV's sales were a result of a decade long hype from Versus XIII, etc.

The cold reception to XVI could be a result of people getting burned out from FFXV since it wasnt what most people wanted it to be on top of the issues that fans had with XVI itself.

I spoke to a lot of none fans and for them it just wasn't on their radar because its the 16 entries into a series that they're out of the loop with. As somone who really enjoyed 16 despite its flaws and saw it as a return to form in many ways, I recommended it to as many people as I could but no one would budge lol.

I think people really understate the importance of the franchise finding new fans. Its not enough that you rely on the 30+ demographic to keep buying your games because many will gradually just loose investment, loose interest in gaming etc

As far as the core fan base I think you legit have almost 2 decades worth of misfires and inconsistency. A lot of once core fans, just don't value the franchise like they used to and seeing FFXVI in action one friend immediately just said "They're still trying to make it an action game"....

I agree that we really need a proper source and verification for this, however I suspect its true. Essentially it has probably sold <4m but more than 3.5m

As someone who follows the charts, you simply did not see FFXVI re-enter the top 20 beyond its launch month. There is no indication that the game went on to have any form of legs which is shocking considering its opening but is probably similar to other JRPGS. 

Its Launch week probably involved 300-500k shipped but unsold physical copies within SE's "3m" figure. Sold those over the following 6 months. Then you have a PC release doing 500-600k... By this time FFVII Rebirth was a few months from launching and I think it had very little legs left. Its probably doing like 10k a month.