I want to chemically castrate myself with androcur. But i dont want to gain weight or lose muscle. Is this even possible?

Androcur - Androkur the instruction for application

https://www.nps.org.au/medicine-finder/androcur-tablets

https://www.myvmc.com/drugs/androcur/

Androcur - weight change?

Cyproterone acetate is an anti-androgen drug. Adverse effects that have been reported with its use include weight gain, depression, fatigue, breast symptoms and sexual dysfunction.

During my time using Depo Provera and later Androcur, I dropped 35+ kg / 80 lbs and kept it off. Now a surgical eunuch. But I cheated. Did diet and exercise.

It is absolutely possible but you will need to be fairly strict with your diet and exercise routine. You will likely notice recovery from workouts will take longer than when you had a higher T level and it may be more difficult to build muscle but not impossible. There are female body builders who maintain physiques that many men would be envious of and provided they don't use steroids (some do some don't) they do so with as low a T level as you'll likely achieve. Keep in mind one factor that could lead to weight gain is the increased fatigue and depression, it's easy to skip a few gym sessions and cheat on your diet if you're feeling down in the dumps so if the weight gain and muscle mass loss is that big of a concern make sure you're already building good diet and exercise habits before you start androcur as that will make it easier to maintain them when you're on it.

My experience with Androcur was, that I actually lost some weight. With fat some muscle mass disappeared as well. I planned my androcur time so that it coincided with a physically active period, so I would have no choice but do what I have to do. Interestingly activities that lasted for a long time but was of low intensity, like hiking, did not feel much different. Muscle loss was felt most when I needed to lift heavy stuff. Also very active movements like playing soccer, made me feel exhausted very quickly.

Interestingly, most of the weight gain happened few months after stopping androcur.

I did put on a bit of puppy fat in the 8 months I had off T and I was still doing 5 mile runs.