flutter doctor checking dart sdk version error code example
Example 1: unable to update dart sdk. retrying
Add below path to Environment variable
User Variables
C:\flutter\bin; C:\Windows\System32
%SYSTEMROOT%\System32\WindowsPowerShell\v1.0\
System Variables
C:\flutter\bin
C:\Windows\System32\
Example 2: unable to update dart sdk. retrying
restart your pc and delete flutter folder in C directroy then reinistall flutter and run flutter doctor