Added in Updates / 7.3 a new city has emerged and with it new missions, items, Npcs, creatures, objects, houses and hunting grounds, along with all this novelty something mysterious has emerged in one of the towers that even today nobody has been able to unveil: "how talk to Npc Arkhothep? "
Updates/7.3 | TibiaWiki | Fandom
An article by Tibia Down talks about Soul Ruby where he says there is currently no evidence within the game and talks about the book by Morgathla and the Serpentine Tower.
O Soul Ruby pode ser obtido ou apenas um mito? · Tibia Down
I believe that it will not be possible to obtain this item because no other player has proved it, as it is a mysterious and legendary item done some research to say that Arkhothep (Ruler of the Dark Pharaoh of Ankrahmun) and Morgathla have the answer however already answering your question.
question: Is it possible to visit and chat with Arkhothep? No, because your tower is currently inaccessible. It appears you can see him from outside of his pyramid, but you cannot speak to him.
"Although your room is inaccessible, there was a screenshot showing it in the Screenshots section of Tibia.com for years."
Image: Tibia - Free Multiplayer Online Role Playing Game - About Tibia
https://tibia.fandom.com/wiki/Arkhothep
"Soul Ruby is a legendary jewel that is said to permanently transform a Helmet of the Ancients into a Helmet of the Ancients (Enchanted). Morgathla discovered this, as can be read in this book. She then shared that knowledge with Arkhothep, who is the only one known to have a helmet imbued with the magic of a ruby soul."
https://tibia.fandom.com/wiki/Soul_Ruby