I didn’t know which category to choose so I chose the top one. I have this blog of mine, which I’m building and some posts could have files that a user could download, is there any API or something that will allow me to create an add to nextcloud button which is similar to add to drive or add to dropbox button you sometimes see on websites
So you want users to download something or add new files to a folder?
You can create shared folders in Nextcloud (read-only or with write permissions) that you can link from your homepage.
With GitHub - owncloud/pyocclient: ownCloud client library for Python, you can use the API to automatize the creation of folders and shares (or have an inspiration for other languages or apps for CMS systems)