$area is NULL for over-wrapping geometry

Question

This question follows from $area gives NULL for some polygons in QGIS's Field Calculator. New question asks the same question as to why some area variables appear NULL. But the problem was resolved for one layer but not the other.
All $areas are found except for the polygon in the screenshot. The larger polygon and smaller polygon are over-wrapped but are separate entries. Area for smaller entry is found but not the bigger one. I tried fixing geometries but it does not help. Please let me know how I can proceed.
I am using the layer, all economic concessions (English) from the link: https://data.opendevelopmentcambodia.net/dataset/economiclandconcessions

Uditha Herath · Accepted Answer

Short Answer
since the $area calculated exceeding the value of the displayable limit of the whole number integer with in field calculator please use output field type as whole number integer 64 bit with maximum output field length of 21
(whole number integer 64 bit and 21 field size is a must)
Long Answer
Please refer the previous answer HERE for the CRS Change and all up to step 4

go to the Attribute Table of the newly created shapefile
Go to Field Calculator
And enter $area in the Expression Field while giving a name to the column with data type whole number integer 64 bit (whole number integer 64 bit and 21 field size is a must)
then give the output field length as 21 (maximum possible)

and click ok
your attribute table should look like this

again as previous areas with unknown geometry will not display any area

$area is NULL for over-wrapping geometry

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