I totally concur with your assessment of Casemiro's skills. In my opinion, he still has a lot to give at the top level, especially at Manchester United. He's clearly been United's biggest loss in the middle of the field, both in terms of defense and helping their front line. He is really missing from the team.
The player's future is uncertain, and moving to the Saudi league now seems like a waste for someone of his skill. He's only 31 years old, so he's still in his prime, and he could seriously help any top European team. These rumors about PSG's desire make sense; they're always looking for top players. He should definitely stay in Europe, where he can continue to compete for big titles, because this is a turning point in his career.
Despite the fact that Casemiro didn't really impress on the pitch at some point, this season before he sustained an injury but there's no doubt he's a very good player with lots of experience when he's fully in form and I believe he still got alot to offer to Manchester United this season, however I think he has alot to work on so as to get better on the pitch when he recovers from injury especially his aggressive tackling that always get him booked.
Well I won't blame Erik Ten Hag, or the board if they decide to cash in on him in the next transfer window, cause they need quick actions and not some constant testing with players that should be performing at their highest peak, but really underperforming and affecting the whole clubs performance with their constant errors, atleast they use the money they realize from his sale to invest in another player that would perform better in that position.