Prerequisites: reordering a non-locked column before a locked column. There could be one or more locked columns.
This behavior appeared in v2021.3.1207.
Dojo example: https://dojo.telerik.com/UhExAXIv/5
The reorder hint appears only when you hover the left border of the ID cell. This makes dropping the header at the right spot difficult, since you have to be very precise and if you are too fast, you have to re-adjust the mouse cursor position right on top of the left border of the cell.
The reorder hint should appear when mouse cursor enters the boundaries of the target cell. For example, slowly drag ShipCity before ShipCountry. Note how the reorder hint appears once you enter the boundaries of the ShipCountry cell and you don't have to drag all the way to ShipCountry's left border.