Is the financing of a project through a partnership, with 85% for the company, and then selling the company's share to the project owner after 3 years at a price higher than its paid-up capital, considered an interest-based loan (riba) or the sale of a common property with an excessive profit?

The decisive factor in contracts lies in their meanings and realities. If the company bears the loss of capital and has its profit, then there is no harm in that, even if there is a promise to sell its share later. However, if the company is merely a financier for a loan with an increment, then this is forbidden usury (riba). Therefore, the mentioned transaction cannot be judged without examining the details of the contract concluded between the two parties.