To structure different projects for the same customer, you can create a collection for that customer and link it with those projects.
You can link a project to a collection by going to the All projects overview.
Choose a project and select Add to collection...
You can select an existing collection or create a new one.
To view all projects within a collection, click on the collection you want to open in the All projects overview.
For each collection, you find an overview of all your projects.
If you choose the Tasks tab in the collection, you find an overview of all your tasks related to this collection. This means if you have several projects related to one customer, all the tasks for that customer are listed regardless of the projects they belong to.
The same view and filter options apply here, so you can structure the collection tasks as you like.