Yes, weight gain is an officially known side effect of antipsychotics. This is due to antagonism (reducing activity) mainly at serotonin and dopamine receptors. It is certainly mainly due to an increase in appetite and possibly also a slowing down of digestive metabolism.
There is also a perfect option for weight loss, which is the use of drugs from the category of Parasympathomimetics (they are not contraindicated with any antipsychotics), one of which can be prescribed by a general practitioner. https://filozofia.nett.to/farmakologia/sk/inhibitor-acetylcholinesterazy-parasympatimymetikum . These drugs, mainly of a neurological nature, act mainly on the brain and the digestive system, accelerating metabolism. Weight loss would be very fast and effective; no dubious natural Viagras (= dubious internet advertisements) have any effect on these drugs. Another positive is that, according to current scientific knowledge, they even improve the symptoms of schizophrenia and can be used as a complementary treatment with these very gentle drugs. Unfortunately, in practice, it will probably be very difficult for a doctor to prescribe them to you; they will not prescribe something they do not understand themselves. They only know the package inserts, and they describe completely amateurish nonsense. In reality, every drug has an indication that is 30 times wider than what is written on the package insert, and these drugs acting on acetylcholine receptors therefore have an extremely wide range of uses.