I put a bunch of toys on the high chair table. My baby hates the high chair too. She tries to stand up from it. I also put her favorite snack on the table so she tolerate it ( teething wafers)
We changed the high chair after months of struggle and it made a huge difference. We got a smaller one that just gets fixed on top of our regular dining chair and tucks in close to the table.
I've got an 11 month old that's worked out how to unstrap herself and stand in her highchair 😭 safe to say we're getting a new one. What I found with my little girl is having small burst of play time in the highchair was really helpful to get her used to it. I say pick a highchair you prefer and get some sticky fidget spinners or something for him to play with in the chair. I would also try eat food with him. Even if it's an apple and make food time a social thing. We found this helpful too