I speculate episode 136 of the Journey's series to happen in at least 5 scenarios;
Scenario 1) Goh tells Ash his ambitions to travel on a journey, and thinks Ash will not want to go with him, only for Ash to tag along, thus they both embark together on a new adventure.
Scenario 2) Goh tells Ash his ambitions to travel, Ash supports Goh's decision, but Goh gets emotional of leaving Ash. Just as Ash and Goh seemingly are about to Goh their separate way, Chloe's dad or Professor Oak informs the duo about some new discoveries in the Paldea region, and this motivates Ash and Goh to continue on as research fellows again, while embarking to a new region and other areas around the world.
Scenario 3) Goh tells Ash his ambition to travel on his own, Ash cheers Goh on, but also reveals to Goh that he (Ash) was invited to visit the Paldea region which is where he will be heading next. Goh then reveals that the Paldea region was the region he intended to travel to as well, and they embark on a journey together.
Scenario 4) Ash and Goh go their seperate ways, with Ash somehow deciding to head towards the Paldea region, after deciding he wants to travel to different regions of the world. Professor Oak or Chole's dad will somehow steer Ash toward a new regional direction.
Scenario 5) Ash and Goh each go their separate ways. Right before Ash sets off, he meets Lugia again and captures it. Lugia becomes Ash's new mode of transportation to venture to newer regions, which he reluctantly goes to the Paldea region by chance. Once in Paldea, he meets Goh again. (THE MOST UNLIKELY SCENARIO)
My biggest speculation so far for a new adventure arc is for Ash to now catch legendaries and mythical pokemon.
Now that Ash is a world champion, he's now like a kid filling in the shoes of a mature adult, which means the pokemon story board writers will now half to up the stakes of his challenges and training if he's to get closer toward his dream. With that said, I dont see a real purpose of Ash catching typical regional pokemon or getting a starter, since he's no longer a novice or intermediate level trainer.
From what we've seen so far in Journey's, besides pokemon trainer battles, legendary pokemon battles are showcased as a grandiose training regimen for strong trainers, and very few trainers are able to defeat mythical and legendary pokemon in battle, especially those that are titan level, such as Mewtwo, Lugia, Mew etc. I'm hoping Ash catches a team of legendaries and mythical pokemon in the new journey story.
My prediction is that Ash's new team will consist of the following;
2) Entei or the new Gen 9 Ancient Area Zero Legendary Beast Pokemon ,
6) Wo-Chien ( The Dracovish of the Group)
These predictions probably wont happen, but oh-boy if it does.