How popular is Kimetsu no Yaiba at west? Every game based on anime that isn't Dragonball, One Piece or Naruto has done nothing special at sales so far and I have a hard time seeing something different this time with Sega being the publisher.
Not necessarily a factor of popularity but
Manga sales data in a couple select markets:
US:
2020 Best-selling mangaka:
01./ Kohei Horikoshi [My Hero Academia] - 1,055,010 (+50.2%)
02./ Koyoharu Gotouge [Demon Slayer] - 557,369 (+380.6%)
03./ Junji Ito [Uzumaki, Gyo, Tomie, Smashed, etc.] - 250,858 (+64.4%)
Compared to 700k for MHA and 115k for KnY in 2019. KnY/Gotouge was 8th in 2019.
2020 Best-selling volumes:
01./ My Hero Academia #1 - 136,491
(+38.2%)
02./ My Hero Academia #2 - 106,259
(+54%)
03./ Demon Slayer: Kimetsu no Yaiba #1 - 80,547
04./ My Hero Academia #24 - 76,151
05./ My Hero Academia #3 - 70,730
(+33.4%)
06./ My Hero Academia #23 - 63,728
07./ Uzumaki HC - 62,465
(+77%)
08./ My Hero Academia #4 - 58,990
(+47.5%)
09./ Demon Slayer: Kimetsu no Yaiba #2 - 53,372
10./ My Hero Academia #5 - 52,393
11./ My Hero Academia #25 - 50,612
12./ Haikyu!! #1 - 50,292
13./ Toilet-Bound Hanako-kun #1 - 48,185
14./ My Hero Academia #22 - 48,173
15./ Tokyo Ghoul #1 - 47,008
(+74.1%)
16./ My Hero Academia #21 - 41,665
17./ My Hero Academia #6 - 40,325
18./ Demon Slayer: Kimetsu no Yaiba #3 - 39,808
19./ The Promised Neverland #1 - 37,060
20./ Demon Slayer - Kimetsu no Yaiba #7 - 35,552
Currently, Demon Slayer is the second/third best-selling manga of the US (in terms of monthly sales for new volumes), behind MHA/on par with JJK.
France:
2020 Best-selling manga series:
01./ One Piece - 2.2m
02./ MHA - 1.2m
03./ Naruto - 1.2m
04./ The Promised Neverland - 0.8m
05./ Demon Slayer - 0.7m (up from under 100k in 2019)
2020 Best-selling manga volumes:
01./ Naruto #1
02./ Naruto #2
03./ Demon Slayer #1
04./ Dragon Ball Super #10
05./ Naruto #3
06./ One Piece #93
07./ My Hero Academia #1
08./ One Piece #95
09./ One Piece #94
10./ Dragon Ball Super #11
As for 2021, Demon Slayer volume 1 has a chance of being the single best-selling volume of the year. But It's going to be hard to top the Naruto volumes (which are helped by their price being half that of other manga volumes - 3€ instead of 7€). It should easily end the year at 250k units sold (more than twice its 2020 total) which is unprecented, though other manga should reach that level (It happened this year because of the manga boom).
As for new volumes, KnY is 4th, behind OP, Dragon Ball Super and MHA. However, KnY is still growing while DBS is stagnating, so that might change soon.
In terms of sales per series, I think it's going to be third. No one will approach One Piece (whose goal should be 5m), but after that, all of Naruto/MHA/Attack on Titan/Demon Slayer have a chance at beind #2 with 2m-2.5m units sold. Imo MHA will stay second, but Demon Slayer should get that third rank.
These are the only 2 markets that I have data for.
But from what publishers have been saying, this phenomenon is worldwide. However, it's a
manga boom. It's unsure if these IP will see their sales elsewhere (video games, merchandising, etc) grow in a similar way.
But KnY is by far the IP that benefitted the most from this boom.
TL;DR
KnY is a top 2 manga IP in the US manga market and a top 3 one in France.
And things should be similar in other countries, with OP and/or MHA sometimes being above (but not always, I recall the KnY manga breaking records at some points in Korea)