Generic sertraline comes in pill/tablet form, you can just use a pill splitter to get smaller increments. I just googled to confirm this before posting, and they're even scored down the middle for easy splitting.
Maybe where you are it comes in tablet form. All capsules in Canada.
(Though in theory the contents should be homogenized, so you could dump the powder and take a proportion of it)
Right, but splitting isn't sufficient for many people. The person I know was on 50mg. They tried to carefully shave off 1/8th initially, then 1/4 etc. It was error prone cutting them exactly and even a 1/8th change in dose at a time with a two week adjustment period caused them to have terrible effects. They cross titrated to Prozac and it became easy to taper down slowly. Reddit and forums are full of people that needed to reduce Sertraline by 1-5mg at a time over a period of months if they've been taking it long term.
I think far more people might find that they need to taper very slowly if more people got past the first step of tapering instead of just staying on them indefinitely. Many people feel more anxious and depressed on a slightly lower dose and take that as confirmation that they were born needing it, when it might be more the case that their brain has adapted to depend on it. If they were able to reduce more slowly and comfortably this might be more obvious. That matches what I saw with the person I know who is finally doing well on low dose Prozac.