It's even disabled by default in the feature bundle for 5.36+

$ perl -e'flush STDOUT;'

$ perl -e'no feature qw( indirect ); flush STDOUT;'
Bareword found where operator expected (Do you need to predeclare "flu
+sh"?) at -e line 1, near "flush STDOUT"
syntax error at -e line 1, near "flush STDOUT"
Execution of -e aborted due to compilation errors.

$ perl -e'use v5.36; flush STDOUT;'
Bareword found where operator expected (Do you need to predeclare "flu
+sh"?) at -e line 1, near "flush STDOUT"
syntax error at -e line 1, near "flush STDOUT"
Execution of -e aborted due to compilation errors.
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(Mentioned in the article.)