PI Vision 2021 Event details attribute selection for trend does not work
It is an offset when you choose the attributes for the trend view in the event details display! You have to pick attributes down the list from the attribute you want to see the trend for.
In the picture you can easily see that the turqoise trend is an Boolean but the displayed value is a float.
This sounds like a bug rather than an enhancement. I suspect it has been fixed in the latest patch release of PI Vision, but I recommend that you work with support to verify this.