This happens sometimes with antidepressants. For some people, it seems to mean that the drug is helpful, but it's just not quite a high enough dose for the effect to stick, and a dose increase will get the effect back properly. Effective doses for sertraline are between about 50mg and 200mg IIRC, so you've got room to go upwards.
Other people sometimes find this happens with several antidepressants, that they work for a little while then "poop out" (I dunno who came up with that phrase, it's gross 🤣), and that for them, none of them really help long term.
I get why you're not keen on increasing but I'm not sure dependency is the best framework to think about this under — it's not the kind of drug where it's standard for people to need to repeatedly increase the dose over and over to keep getting the same effect, like can happen with benzos or opioids. More that if you're on a dose that's not quite enough for you, you might get some effect but not all.
Being on a higher dose probably won't make you more likely to have difficulty coming off them, as far as I know (though if you are one of the unlucky people who has bad symptoms when stopping, it might take a bit longer to gradually taper off).
Talking therapies, lifestyle changes, hormonal investigations and all the things others are suggesting are also good, either instead of, or as well as, antidepressants.
But if it were me in your position, I might be reluctant to back off from the antidepressants without giving them a chance at a higher dose, when they've already shown they can help, albeit temporarily, at this dose. Sometimes it's easier to access and make good use of things like CBT, or put in place helpful lifestyle changes, when you've got a bit of help from antidepressants, for example.
On the other hand, recovery without medication can often be done, and it might be that antidepressants aren't for you. It's entirely your choice obviously.
I feel like it might be a good idea not to set aside any reasonable options at this stage, if that makes sense?