>>52452356“Champion” is a role and a title.
The reigning Champion is top dog of the competitive circuit, and that is their role - to challenge trainers who defeat the Elite 4.
Champion is also a title for anyone who has ever beaten the reigning Champion, or is no longer in the role. You become A Champion by defeating the THE reigning Champion, or was we saw in RGBY and SMUSUM by defeating an Elite 4 who doesn’t have a current reigning champion.
Not everyone with the title will take up the role, because they either gave up the role for personal reasons or losing to the new Champion, or they don’t want to be stuck with the responsibilities of the role (every protagonist besides Gen 7).
Gen 9 just made it more apparent. The Top Champion is the reigning Champion in the role, and is the final battle in becoming a Champion. Characters like Nemona have the Champion title, but not the Top Champion role - presumably because Nemona isn’t content being the strongest and doesn’t want to sit around waiting for a challenger to finally catch up with her.
Even Geeta herself said that Nemona could woop her ass anyday she wanted to, but Nemona obviously doesn’t want the role. If a Champion-ranked trainer would seriously want to take the Top Champion role and its responsibilities, they’d probably have to be further assessed and champion La Pageeta’s team yet again.