How are the real profits for an investment in a store calculated when the partner offers a lump sum of 10% of the invested amount (100,000 Riyals) without referring to the actual profits?

Guaranteeing a specific percentage of profit, regardless of whether it materializes, is impermissible and transforms the transaction into an interest-bearing loan. It is also impermissible to set a fixed amount of money as a partner's share, otherwise, the partnership becomes void. If you participate with 100,000 out of 600,000, you own one-seventh of the capital, and the profit from this one-seventh is divided between you as per your agreement. If you do not agree on a profit percentage, then you are entitled to a customary share (qirāḍ al-mithl), and the worker is entitled to a customary share. You both must rectify the contract by specifying each of your shares in the profit.