Very odd. Thinking to step ouside of Linux, I tested this on Windows. It appears to have worked correctly for me as well.

SKMDSK06::T:\>perl -V | findstr uname
    uname='Win32 strawberry-perl 5.32.0.1 #1 Sun Aug  2 19:46:04 2020 
+x64'
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SKMDSK06::T:\>set user
USERDOMAIN=SKMDSK06
USERDOMAIN_ROAMINGPROFILE=SKMDSK06
USERNAME=Steve
USERPROFILE=C:\Users\Steve
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SKMDSK06::T:\>type test01.pl
use strict;

use Path::Tiny;

my $path = path("/a/b/c/$ENV{USER}")->absolute;

print "$path\n";
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SKMDSK06::T:\>perl test01.pl
T:/a/b/c

SKMDSK06::T:\>
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Not sure that this helps any, but there it is.