This is still debated among economists: so there is no clear answer to this.
i would only give some arguments:
- they do seem to work, because after the situation in Crimea in 2014, the conflict did not get worse
-On the other hand: Russia did not withdraw from Crimea- so they did not work completely.
In general, I would say that the sanctions are rather aimed at specific event (forcing Russia to stop the war in Ukraine) than weakening it: since the sanctions also harm other countries. And if we evaluate them with respect to this, i would say: they are effective in "reminding" Russia that not everything is allowed, but do not weaken Russia significantly.