Like, the animation style and sense of humor just feel entirely different, sometimes not even bad, but just not something you'd think "Yeah, that's a joke from Spongebob".
I can't exactly describe why, but the show just doesn't feel like "SpongeBob" anymore. Even at its previous lowest, during seasons 6-8, the show still felt decidedly like it was still "SpongeBob" in spite of the gross-out/shock humor. Some of what I've noticed contributes to it is a much more ADHD animation style, where it feels like there has to be something bouncing around, or flashing colors, and loud noises, all the time (like Teen Titans Go).
There's never anything like the early seasons anymore where they just paused everything with a simple sound effect to let a joke land, like in "Shanghaied" with the "I'm getting to the bottom of this thing!" "Wouldn't that be the top?" bit. The "jokes" themselves aren't even jokes, there's minimal attempts at any kind of actual humor, they've returned to gross-out and shock content, but now it's not even trying to be funny, just attention-grabbing.
Then there's also the "stunt casting" as it's called, where they bring in actors just because they're famous, rather than a good fit for the show. They brought in famous actors all the time back in the day, like Pat Morita (Karate Kid's Mr. Miyagi) as Master Udon in Karate Island, or Thomas F. Wilson (Back to the Future's Biff) as the bouncer at the Salty Spitoon, but they fit the show's tone really well. You typically wouldn't know that these were special guest actors because they fit into the show so well. Now the show frequently uses voice actors that sound completely out of place, with the 3rd movie being a serious offender. While Matt Berry is great (he was in the second movie too), the movie also has voice actors like Awkwafina and Tiffany Haddish who sound completely out of place.