Is the participation of a doctor in the "Doctors' Treatment" project, which grants him discounts on medical services in exchange for an annual fee, considered a prohibited form of insurance?

If the subscription is based on cooperation, mutual support, and donation, then there is no harm in it. However, if it is based on financial profit, then it is unlawful due to the presence of gharar (uncertainty) and risk. This type of subscription falls under the category of selling discount cards.