The biggest issue I have with the later seasons is that the show constantly walks back major character developments and beats in favor of whatever random nonsense Royland and Harmon have come up with that week.
Beth's entire arc in season 3 was realizing how similar she was to Rick, along with all the toxicity and irresponsibility that implies. But now in the newest season, she's suddenly a super caring mom who is so much more supportive and caring of Morty than she's ever been. She acts more like season 1/2 Jerry than any version of Beth.
Shit, season 4 seemed to end with Beth finally moving beyond Rick, realizing what a shitty dad he was. Yet, their relationship is back to being mostly stable now. Sure, she calls him out in the Decoy Family episode, but she's nowhere near as pissed at him as she should be if the development was consistent.
Morty oscillates between being a stone-cold psychopath who kills anyone that gets in the way of his short-sighted goals, and a naive kid who doesn't get why unleashing and then dating Planetina was a bad idea. The scene where he acts all shocked as Planetina murders the coal workers is such a bizarre scene because, like, dude, Morty has killed literally millions of people both directly and indirectly at this point. And he draws the line at Planetina killing a few mining workers? It's so inconsistent.
Hell, the Planetina episode is basically a worse retread of the Fart episode. Both involve Morty getting involved in a complex situation out of a desire to do a good deed, only for him to discover that in his desire to be a hero, he ended up making the wrong decision. It's almost the same exact character arc, just with a few notes changed here and there.
And all this comes from the show's bizarre attitude that it doesn't need to have continuity or an actual throughline. The train episode was basically the writers pointing and laughing at anyone who thought or wanted the show to have those things. But now the joke is on the showrunners, as it's clear they're quickly running out of new ground to cover because the characters can almost never majorly change. And any change that does stick is invariably a negative one, which just makes the characters more and more unlikable by the episode.
By this point, I have a hard time caring about any of the major characters. They've all gone from assholes with redemptive qualities to just plain ol' assholes. Any moments that try to inject vulnerability into the characters, like Morty's breakdown in the Planetina episode, just feel cheap at this point because none of these characters are geared towards kindness or vulnerability.