I believe that the dev used  RPG Maker XP (available on steam and the official RPG Maker website) with pokemon essentials (a modified rpg maker xp project, you have to buy rpg maker before downloading essentials, you can find it by searching it up or on something like eevee expo or pokecommunity )? I would recommend watching Thundaga's tutorial series for pokemon essentials on youtube if you're learning the engine from scratch. For making sprites, you could use something like aseprite, krita, or photoshop.
Game dev stuff tends to be pretty difficult and time consuming, so I wish you the best of luck in your endeavors!