Unfortunately, by reading your description I'm not able to reproduce this problem. Could you please provide a working example in an online editor and describe when exactly does this problem occur? You can share your soluton by using this demo: https://jsfiddle.net/BlackLabel/dgq8bemv/.
when i use dragPrecisionX: day, after dragging the end point to a particular date (for example dragged to 24/03/2023 ) it was considering the next date (25/03/2023) as end for the task, but I was trying to get (24/03/2023) as end date.
Please refer the interactive Gantt demo and change dragPrecisionX as day and drag the end point of any task then you can have clear view on the above question
I've been able to reproduce your problem and with a simple override using Higcharts.wrap it's possible to achieve what you've described. When the end date position changes (when dragging whole bar or just its end), by substracting 1000 ms (1 second) from the end value, the end date changes to last minute of desired day rather than midnight of next day.