The first opportunity to develop a new leader is to assign them to lead a special project. There are many examples of special projects that need to be done – updating processes, changing software, updating the culture playbook, or making a plan for a big transition. Assign that special project to your potential leader to run, and make sure they have a team to lead, as well.
Another leadership opportunity is to have your potential leader take the reins when you take a vacation. Clearly communicate to everyone on the team who the leader will be while you’re away. Then go on vacation! If an employee contacts you while on vacation, redirect them to the individual you left in charge. The person you left in charge should be the only one who contacts you while you are out of the office. How often they contact you during that time can be an indicator of if they are ready for leadership. IF you can’t take a vacation, that exercise is still a good one to go through even while you are in the office. Maybe you assign that person to take the lead for a couple of weeks while you finish a special project of your own.
Another opportunity you can extend to this potential leader is asking them to mentor a newer employee. I would suggest giving the potential leader a road map for mentoring, but then step back and watch.
A few other ideas would be to have this potential leader take over leading staff meetings. Or you can ask them to take on learning and education projects where they are responsible for training a room of their peers, and then holding their peers accountable after the training ends.
Those are just a few ideas. If you are still unsure of what opportunities for developing your new leader, delegate one of your own leadership duties to them for a short-term period, and see how that goes.