There is no way to change it through the ACP, you need a theme or a plugin to override the breadcrumbs & page title. Maybe nodebb-plugin-customize can help.
Let's say I have 10000+ categories... And only shows 10 of them and load more with pagination... I also need to search the category by typing the name of the category if there are too many.
Is this possible? What Nodebb does for such case in order to handle too many categories?
NodeBB by default doesn't do anything when a lot of categories are present. There is no pagination on categories page, no sorting or filtering and no searching for a category.
If you want to handle a lot of categories, you have to do it yourself. I started working on a plugin for filtering and sorting categories some time ago, but it's far from being finished (basic sorting works, but there is no acp for setting up filtering and sorting rules - you just have to modify them in code. And you have to manually add the sorting as a widget to categories page). I'll probably publish it somewhere here when it's ready, but for now and for other functions you want - you unfortunately have to make them yourself.