how can I render OpenExr 16 bit float

Since ProEXR is the same as After Effects standard OpenEXR plug-in, the ProEXR manual is helpful.
According to the manual, if 32-bit float is not checked, it will be rendered as 16-bit float.

32-bit float!By default, OpenEXR stores pixels in a 16-bit float format. This is usually ideal, but
if you have a need for 32-bit float pixels (perhaps because you have values over 65,504.0?),
check this box. Otherwise it will just increase your file size unnecessarily, which is why it’s not
recommended. 32-bit is not available in conjunction with Luminance/Chroma.

＊ All functions are included in ProEXR, so you can replace it with an After Effects plug-in.

After Effects supports OpenEXR.

Premiere can be supported by installing the plug-in "ProEXR".

https://www.fnordware.com/ProEXR/