Hello,
You can look into using a Navigation Invoker. This is a component that you can attach to your character.
The great thing about invokers is that they allow you to use large levels without having the wasted performance of a large, unnecessary Nav Mesh.
To start, go to Edit->Project Settings->Navigation Mesh and set the Runtime Generation to dynamic. Also, go to Edit->Project Settings->Navigation System and check the Generate Only Around Invokers option. Then, you’ll need to add a Nav Mesh Bounds Volume to whatever area you will be generating your level in.
After you’ve done this, go into the character(s) that you’d like to be able to use the Nav Mesh and add a Navigation Invoker component. This will allow you to alter the settings however you’d like as far as how far you want it to generate and how far away you’d like it to be before it begins removing the unused sections of the Nav Mesh.
Let me know if you run into any trouble with this.
Have a great day