Is the money received from the restaurant's rent lawful in this manner, especially after settling debts with the invested money, and can the amount be claimed back upon dissolution of the partnership, and how can Sharia violations be rectified, and is it advisable to reclaim the money and dissolve the partnership in case of doubt?

The aforementioned partnership is permissible, whether the purpose of the rental is profit or leasing the restaurant to others. The profit share will be according to the agreement, while losses will be borne in proportion to the capital. Partnership involving assets (non-cash items) is permissible according to the Maliki school, some Hanbalis, and Shafi'is in fungible items, provided that the assets are appraised at the beginning of the partnership. If you give money to your partner to pay off his debts, it is a loan and does not enter into the investment, and stipulating a profit on it is forbidden usury (riba). When dissolving the partnership, the assets are sold or appraised, and their value is added to the cash liquidity so that each partner receives his capital. If the partner takes your money to pay off his debts in exchange for your share in the restaurant's rent, this is usury. The permissible solution is for him to sell you a part of the restaurant, making you a co-owner, and you then divide the rent.