Which sidehustle realistically brings in additional income?

Yes, actually everything is in the headline. I would be willing to trade free time for time to make more money. I have a full-time job and am happy with the salary there, but as an employee, big jumps in the future are rather unrealistic. That's why I would like to invest time in building something on the side or improving my income. It's not about unrealistic wishes, I would be happy if, for example, I could pay off part of the fixed costs (home loan