IE: Gen 1 RBY and most of Gen 2 GSC outside of a couple of details(1997 Spaceworld GS is pure Tajiri Canon).
This is the world of Pokemon as Tajiri saw it, with lore details lurking in a 1996 Canon-to-RBY handbook that only Japan got (translated by DYKG on Youtube) and the manual and small in-game details.
This world of Pokemon was our world, except in the 1800s a new class of creature called Pocket Monsters was discovered by a french dude and research on them surged in the 1900s. (And Tajiri in Japan ALWAYS used Pocket Monster, Pokemon was purely a legal issue at the time and Japan only started using it alongside Pocket Monster in Gen 3 after he left) and a few locations were changed.
Pokemon were a newly studied class of animal or creature that people were still actively learning more about(the book is set in 1995 like 6 months before the game and yet only 130 species have been discovered and the link between Venomoth-Venonat and Magikarp-Gyrados is still unknown to science).
Real world animals existed and their relationship with Pokemon was often discussed. Real life countries like France existed. Japan of RBY was actual 90s recession Japan with all it's problems, hence being set in an alternate version of the Kanto Plain. Mew was found in FRENCH GUIANA(not Guyana Guyana mistranslation). Team Rocket has a branch in Siberia.
Legendary Pokemon are just that, Pokemon of Legend and Myth with a lot of historic status. Not gods. IRL religions exist, there's a Shinto Temple in Celadon in Red and Green that was censored in the west, and the handbook alludes to Abrahamic Religion.
Tajiri saw the Pokemon world as a semi-realistic urban fantasy setting based on 90s Japan, showing off some of the Urban decay and youth crime problems he saw and the loss of green space around cities. Pallet Town being a refuge for that lost simpler time of his childhood.
This is massively, MASSIVELY different from Masuda Canon and worldbuilding. Masuda saw the Pokemon world as it's own completely new setting and world, and cut away a lot of the dark underbelly. It's closer to Solarpunk if anything else. No more IRL nations, no more IRL animals, no more IRL religion, Legendaries are gods now and there's a new mythos and creation story.
The difference is best seen in how new Pokemon are handled. GSC treat the 100 new Pokemon as genuinely brand new discoveries, hence no regional dex, just an 'updated Pokedex order' and 'un-updated pokedex order'. Pokemon Eggs are also a brand new discovery by Elm and Mr. Pokemon. Meanwhile in Masuda canon Gen 3 onward new Pokemon always existed and we just never saw them. You can see the games and anime change the way they talk about new mons, and even HGSS changed a ton of lines about Eggs and the new mons to discard them being brand new discoveries because it no longer fit the canon.
EDIT: See that book translated here https://www.youtube.com/watch?v=7yy0lzgXAgw
by Sailor_Rout