This is a topic change, but I've genuinely never understood why people make out like being a Pokemon master is something unknowable.
Quoting Bulbapedia's article on the matter:
Pokémon Master (Japanese: ポケモンマスター Pokémon Master) is a title in the Pokémon world. It is the goal of many Pokémon Trainers to become a Pokémon Master. However, exactly what this position is and how one attains it is vague and never fully explained.
In response to an email sent to its mailbag, Pokémon.com posted the following:
I get why the Pokemon Company would be reluctant to define it in such terms - it may be that the very fact that people were curious enough to ask made them decide "yeah, let's string this out." However, I’ve honestly never seen why it’s supposed to be such a mysterious and undefined goal.
The early anime does admittedly muddy the waters with Ash (and the narration) declaring that he will catch every Pokemon and thus become a Pokemon master. However, even back then it was always my interpretation that this is the metric
by which Ash himself judges will make him a Pokemon master - it's not a concrete "obtain all 151 Pokemon and you're golden", otherwise any wealthy person could do it with relative ease, and Gary gets explicitly called out for catching over 100 Pokemon but not taking the time or effort to bond with them and raise them all.
To me it’s pretty clear that to be a Pokemon master is simply to be an elite. Analogous to someone who’s reached the peak of their profession in any other field. Someone whose mastery of Pokemon battling, raising, and/or knowledge is so extensive that they’re considered one of the best. They don’t necessarily *have* to be an Elite Four member or a champion, it's just that a lot of them are - but we've seen trainers in the games and anime who absolutely should count as master trainers who often have no particular position or rank. No, it’s just being incredibly good at what you do - akin to being an Olympic athlete or a chess prodigy.
This is why Ash thinks that forging a special relationship with every species of Pokemon there is (and to give him his due, he has shown that he's really good at drawing out the potential of pretty much any Pokemon he catches) is what will make him a master. That's his personal ultimate goal. He has also always wanted to be a fantastic battler and achieve recognition for his prowess in combat but that's ultimately concomitant with his primary goal of catching them all, despite the direction of the recent anime. But I haven't seen most of Journeys so I won't expound too much on something I still need to be more familiar with.
But to circle back. What a Pokemon master is may not ever have been fully or properly explained, but I don't think it's something that is difficult to deduce when you look at everything the series has told us so far.