Is personal financing offered by Qatar Islamic Bank, which is secured by salary and involves paying a specific amount of money to the customer, then recording a debt against them that is greater than the amount paid after buying and selling shares to add a profit margin, considered usury? And what is the difference between Sharia-compliant financing structures and usurious personal financing transactions?

There is no objection to dealing with a bank that first purchases and owns shares, then sells them to the one who ordered the purchase, even if it is for more than their market value. The bank may also authorize the client or a brokerage firm to make the purchase. If the client owns the shares, he may sell them himself or by authorizing a brokerage firm for the purpose of tawarruq. As for usurious banks, they lend to the client with usurious interest, which is forbidden by Islamic law, unlike the profit resulting from permissible sale, in accordance with the Almighty's saying: "Those who consume interest will not stand [on the Day of Resurrection] except as one stands who is being beaten by Satan into insanity. That is because they say, 'Trade is [just] like interest.' But Allah has permitted trade and forbidden interest. So whoever has received an admonition from his Lord and desists may have what is past, and his affair rests with Allah. But whoever returns [to dealing in interest] - those are the companions of the Fire; they will abide eternally therein."