Hi again!
I will tell you what I would do if I were in your place.
But please take this with all the grains of salt in the world, as I am by no means a medical professional! (Just saying this in case you want to sue my ass or hate my guts later on 😄).
Since you are only on day 4 of the cut, you still have options, which is great. It is generally not advised to make these big 50% steps, and while there is no rush to reinstate or drop the dose right this second, I would really like you to read up on the advice from this forum (or the old Surviving Antidepressants forum, which is read-only now). If you got the 50% advice from your doctor, just know that they often operate on outdated info—and well, as you said, there is no lower-dose Zoloft on the market (France is the same, which is a frigging shame).
So, with all of that said, and based on everything I've learned, if I were in your shoes, here is the order I'd tackle things:
1. I'd reinstate to the older 50mg dose to stop those side effects from escalating.
2. I'd hold there for a good amount of time until I was fully, 100% stable again.
3. While stabilizing, I'd educate myself. I'd read the guides here on safe, hyperbolic tapering and watch a few YouTube videos from folks like Anders Sørensen, Dr. Josef, and Mark Horowitz to really understand the science.
-->
https://taper.community/resources/blog/zoloft-withdrawal-symptoms-and-timeline
4. I'd check in with my body, mind, and soul to figure out what my personal, long-term plan should look like moving forward.
5. I'd ask that Gigi person from the internet how she makes her liquid or I'd google "water taper Sertraline" 😉
6. Once I was ready to taper again, I'd order some simple things off the internet that allow me to make liquid Sertraline myself at home.
Again, you need to check what I said against your own intuition, but given that you found your way here, I assume you already have a slight idea that the path you are on feels a little "off."
P.S. One last thing! You might also want to look into compounding pharmacies. They can actually make custom liquid or custom-dose capsules for you if you get a prescription. Just another option if you don't want to go the DIY route!