How can one make sincere repentance and return to Allah Almighty while there are rights of people that are difficult to restore, and what about unfulfilled vows, missed prayers, unfasted days of Ramadan, and expiation for backbiting?

You should hasten to sincere repentance, for Allah forgives all sins if their conditions are met: abstaining from the sin, regretting it, resolving not to return to it, and restoring rights to their owners or seeking their forgiveness.

If you are unable to restore financial rights to their owners, they remain a debt on your conscience until you are able to repay them. If you die before fulfilling them with a sincere intention to repay them, Allah will fulfill them on your behalf. If it is impossible to identify the owners of financial rights or reach them, you may give charity on their behalf while guaranteeing their rights should they be found later.

As for non-financial rights, such as backbiting, it is sufficient to supplicate for their owners, seek forgiveness for them, and mention their good qualities, unless seeking forgiveness would lead to a greater harm.

As for the expiation for oaths, you may fast three days if you are unable to do otherwise. If you are not certain that it is obligatory upon you, then there is nothing upon you concerning it.

As for missed prayers, they must be made up by estimating what is most likely to clear your conscience.

And if the university grant is the student's property without conditions, then it is his right.