What is the most appropriate way to ask user to select few (10 for example) categories from a list of thousands to proceed with the app

I am working on a mobile app which relies on the categories/themes of interest chosen by the user and show content accordingly.

These categories are coming from another website and are similar to the numerous stackexchange forums i.e. you must choose what content you have to see. In my case the overall number of categories could be 1000s, however many of them may have overlapping content.

The idea is to have the user select a minimum of 10 such categories before moving to the main app content. The content is based on the user's selections.

How can I let the user begin exploring the app's content without taking a lot of time with selection of categories.

I am currently showing the whole list to the user. However since the list is huge, I feel like the user may lose interest before even starting.