ATM there is no reason to withdraw money at all unless you for some reason get very desperate, and the fact the money goes straight into your active inventory gold means the banks are basically: Deposit some money > completely forget about it. Unless you dd more money to it later. This makes it so the withdrawal fee is basically a non issue. If the money went into the bank balance itself, it would make it much less overpowered than it currently is, and make the withdrawal fee have an actual impact, and give you a reason to keep going back to the banks to withdraw profits.

On that note, and I don't know if this is possible, but you could also link it so you only get the trade XP when you withdraw profits, which would give you more reason to return to banks instead of ignoring them after deposits

negative interest rates would be cool. depending on prosperity
chance for a robbery if town is low on secruity is another thought.
but maybe thats against the spirit of the mod.

Thank you for your suggestions.

RagingLooney: I have not had the time to update the mod for a while, albeit I just updated it. I do no longer play Bannerlords, but I like your idea! I do not promise you will see this soon, as I have a few exams to focus on, but it sounds like a great idea.

Letheral: I had thought about the idea of loosing money in some ways, as this mod is very overpowered late game. I figured that to make it fair, you should be notified that a robbery might take place in this or that town, and you could go there and fight off the robbers. However, that is out of my capabilities and time for the moment. The source code is on github, and I will cheer you on if you attempt to implement this yourself!