no enough disk space available when I install Xcode 12.1

I upgraded to Mac version 10.15.4
Then, I install Xcode 12.1 from apple store. But ,it is showing "There is not enough disk space available to install the product" like attached screenshoot.

However, my Mac remains 39.26 GB available .
Why apple store is showing not enough disk space available?

APFS shows weird amounts of free space that you actually do not have. Look in Disk Utility.app to get an accurate reading.
no enough disk space available when I install Xcode 12.1
 
 
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