These two things do not line up with each other. Gains from testosterone can’t be kept? But gains from experimental drugs can? Where does one acquire this sense of self-assuredness without any actual evidence?
Gains from testosterone are as keepable as it gets, my man. Especially over a 12+ week cycle. With good diet and training (and assuming a competent and successful PCT) you can keep a lot of your gains from many, many AAS and/or SARMs. I don’t know who told you otherwise but you should laugh at that person and then never listen to them about anything ever again.