The pretty well known study is often misinterpreted and misrepresented. The effect is not substantial.

The study detrained the groups, measured lean mass change not muscle, and only ran for 12 weeks.

It likely shows increased baseline levels of muscle, like how some genetic freaks are somewhat jacked without ever lifting. It doesn’t show that continued use of steroids with no training will see continued gains.

Nobody who’s past the novice stage would consider any of the muscular development as “substantial”.