Is it possible for a sin such as masturbation, which has become an addiction and is difficult to stop despite attempts and resorting to solutions like exercise, fasting, and avoiding women, to be a trial from Allah, or is it a product of one's carnal desires?

Masturbation is a reprehensible habit with negative effects on its practitioner religiously, psychologically, and physically. It does not treat the problem of lust. The servant's persistence in sin leads to becoming accustomed to it, and sins breed their likes and generate one another. Citing divine decree (al-qadar (definition)) as an excuse for committing sins is a wrong approach and contrary to both Sharia (definition) and reason.