Is offering a person an investment of EGP 50,000, on condition that 30% be returned monthly and the profit and loss be shared, then ceasing payment due to the car being stolen, considered a project with a doubt of Sharia impermissibility?

What transpired between you two is a contract of qirad (profit-sharing) or mudharabah (commenda), which is permissible if it fulfills the conditions. The most important of these conditions are: specifying each party's share of the profit, and sharing in the loss. The loss for the capital provider is in their wealth, and the loss for the mudharib is solely in their effort and work, without guaranteeing the capital unless they commit an تجاوز (transgression) or تفريط (negligence).

If the agreed-upon share is from the profit and not from the capital, and it is taken monthly, then there is no objection to it. Profit becomes due upon its manifestation and is owned upon liquidation or valuation. It only becomes binding upon division. It is permissible to distribute the project's income that generates revenue, and what is distributed before liquidation is considered an advance payment. There is no legal impediment to using valuation to determine or distribute mudharabah profits. This distribution becomes final upon the realization of mubara'ah (mutual release) between the partners.