I put both of my kids 529 in the high school graduation date fund which gradually went from aggressive when they were in single digit age to basically money market/short term bonds at graduation date. The timing couldn't have been worse. My oldest daughter graduated high school in 2020 and the fund switched to mostly money market/short term bonds right at the bottom of the covid selloff. So she locked in losses there. Then the market went gang busters for the next 4 years and she didn't participate much in that gain. Also the first couple years the fed rate was 0 so all of her bond funds were paying very little. Then in 22 fed funds rate exploded, causing her to lose some money in those 'safe' bond funds.
My second daughter graduated in 2022 and had similar problems where the fund went to all money market/short term bonds when fed funds were at 0%, and then fed funds rate exploded and so she lost money in those 'safe' bond funds.
I'm not advocating any kind of strategy, just saying that even with the best of intentions, things can go to ****.