Aha, I see. Well, you're not wrong about the meaning of the word démultiplier.
In a mechanical it does mean “to slow something down with force”. In a non-mechanical sense, it means “to increase the power/effect of something by leveraging different means”. When we make the verb reflexive (se démultiplier), then we get the sense that the subject is using more resources/effort to do something.
We can also break the verb down a little more (if it helps).
Multiplier - simply means to multiply, obvious enough.
Se multiplier - means “to reproduce” in its most basic sense. However, it also carries the figurative meaning of “to undertake many activities simultaneously, seemingly being everywhere at once, used when talking about someone very active”.
Dé- as a prefix can have several meanings:
- Used to indicate the reverse meaning of the verb (not applicable in this case),
- Used to indicate the removal of something (not applicable in this case either),
- Used to reinforce the meaning of the verb (this is the one!)
If we take the third definition of the prefix dé- and add it to se multiplier then we understand the verb as describing someone who is all over something (an activity, an idea, a job etc.) and is over-invested in whatever the task happens to be.
I hope the breakdown helps,