I say this a lot, but I was a huge fan of Tyler O'Neill for most of his Cardinals' career, and I still believe he can be an impact talent at the Major League level. Even so, it is clear that he will not be back with the Cardinals in 2024.
That's the right decision as well. O'Neill just does not play enough games to continue to roster, and even since his breakout in 2021, he's been an average player at best. When he's not on the IL, there are issues with him being scratched from lineups and not feeling ready to play, and I just do not see the Cardinals dealing with that again next year.
He's due an arbitration raise this offseason, which would likely be around $6 million or so for the 2024 season. Honestly, unless the Cardinals have a suitor lineup up early in the offseason to trade for O'Neill, my guess is they non-tender him to save that money from their books to spend toward starting pitching.