The Famitsu sell-through for all the versions of DQXI currently stand at around 3.90 million units in Japan, that's without counting the digital copies sold.

Total shipment for mainline Dragon Quest games in Japan:
Dragon Quest IX DS 4.40M
Dragon Quest VII PS1 4.14M
Dragon Quest VIII PS2 3.80M
Dragon Quest III NES 3.77M
Dragon Quest VI SNES 3.19M
Dragon Quest IV NES 3.04M
Dragon Quest V SNES 2.79M
Dragon Quest II NES 2.41M
Dragon Quest I NES 1.50M

Sales-wise DQXI fall in line with past DQ games however what's different compared to the past is how they had to achieve those sales (by having to develop multiple SKUs).

In the past DQ appeared on the platform that dominated the japanese market instead with DQXI initially the game was thought as a PS4 exclusive, with the custom 3DS version created later in production due to Square Enix fearing that PS4 couldn't sustain the kind of sales expected by a mainline Dragon Quest game.

https://nintendoeverything.com/dragon-quest-xi-was-originally-ps4-only-3ds-version-was-added-later-on/

EDIT:

While the double/triple dippers concern is valid, I hope I don't need to explain that a game sales won't scale proportionally with the addressable install base.

What matters is the number of people who own those consoles for which the game is available who deem the purchase of the game as worthy of the asking price.

I don't know why the development story matters. If Dragon Quest maintained popularity, XI should have performed better than it did. I predicted around 6 million across the three version, because each one offered things the other lacked, encouraging double/triple-dipping. DQXI PS4/Switch and 3DS are essentially each other's remakes. Being accessible to a larger playerbase is the other factor to consider.

Don't worry you don't have to explain that lol. You'd be hard pressed to find anyone here who spoke against gauging success or popularity based on attach rates alone more than myself. But in the case of Rise vs World, the inevitable 300%-350% install base advantage of Switch over PS4 should be expected to translate to more than the increase we're seeing. I was expecting it to sell 4.5-5 million, which is a conservative figure compared to what many others thought here.

Going by attach rates, nothing beats World which launched to a ridiculous 33%~ attach rate at 6 million PS4's, and pretty much maintained it. I hoped that this was an indicator that the series may be growing in Japan (Peak popularity Monster Hunter sold an unimpressive 1 million on Wii), but Rise is under-performing all things considered. Rise launched to an (expected and fairly impressive) 10%~ attach rate, but it's not legging out particularly well with the install base in mind (slightly/moderately worse than I expected, but not exactly a shock).

The relationship between install base and software sales is certainly not proportional, but it's linear. The popularity of Switch just isn't being reflected on Monster Hunter Rise so far, and this indicates a slight decline in the IP's popularity in Japan.

It's actually kind of funny that Capcom refuses to release a Monster Hunter game on both Playstation and Switch. Would likely break Portable 3rd's record, but probably not when counting PS3's version.

I don't know why the development story matters. If Dragon Quest maintained popularity, XI should have performed better than it did. I predicted around 6 million across the three version, because each one offered things the other lacked, encouraging double/triple-dipping. DQXI PS4/Switch and 3DS are essentially each other's remakes. Being accessible to a larger playerbase is the other factor to consider.

Don't worry you don't have to explain that lol. You'd be hard pressed to find anyone here who spoke against gauging success or popularity based on attach rates alone more than myself. But in the case of Rise vs World, the inevitable 300%-350% install base advantage of Switch over PS4 should be expected to translate to more than the increase we're seeing. I was expecting it to sell 4.5-5 million, which is a conservative figure compared to what many others thought here.

Going by attach rates, nothing beats World which launched to a ridiculous 33%~ attach rate at 6 million PS4's, and pretty much maintained it. I hoped that this was an indicator that the series may be growing in Japan (Peak popularity Monster Hunter sold an unimpressive 1 million on Wii), but Rise is under-performing all things considered. Rise launched to an (expected and fairly impressive) 10%~ attach rate, but it's not legging out particularly well with the install base in mind (slightly/moderately worse than I expected, but not exactly a shock).

The relationship between install base and software sales is certainly not proportional, but it's linear. The popularity of Switch just isn't being reflected on Monster Hunter Rise so far, and this indicates a slight decline in the IP's popularity in Japan.

It's actually kind of funny that Capcom refuses to release a Monster Hunter game on both Playstation and Switch. Would likely break Portable 3rd's record, but probably not when counting PS3's version.

Pretty sure Nintendo paid for console exclusivity and published it in the west. Otherwise there's no way they wouldn't add a PS4/5 version alongside the PC 

Pretty sure Nintendo paid for console exclusivity and published it in the west. Otherwise there's no way they wouldn't add a PS4/5 version alongside the PC 

Monster Hunter has had two separate lines long before World, with the numbered entries and Freedom Unite 1-3 + Generations.

I guess they just want to stick with what has worked for them for so long, in addition to likely some generous moneyhatting from both sides.