Can't Output Entries from Particular Blog Categories
First you'll need to know what you are currently doing

craft.categories.slug()


Will return a CategoryQuery with no property attached to it. So when you execute this query you'll fetch all categories. Your so called category variable is no category but a query that needs to be executed in order to do something

craft.entries.relatedTo(category)


Same thing again: it will return an EntryQuery with all entries that related to any category in any field. So as long as an entry has a relation to what every category it will match. Then again entries is not an array of entries but a query that needs to be executed via all()

When you loop through this query it is executed as well but with a deprecated warning because this way is not supported anymore.

If you are in a category page you'll likely have the catetory variable already injected as superglobal in your template. So there is already a category you have access to.

You can then do

{% for entry in craft.entries.relatedTo(category).all() %}


Please make sure there are entries that are related to your current category