I don't know which system you're on, but GNU bc does not support this flag.
On the other hand, bash and zsh support this:
bc -l <<<'(2/3) * 3 - 2'
On the other hand, bash and zsh support this:
bc -l <<<'(2/3) * 3 - 2'
bc -v
bc 4.0.2
Copyright (c) 2018-2021 Gavin D. Howard and contributors
Report bugs at: https://git.yzena.com/gavin/bc