I don't think NextCloud and Dropbox are not in the same category for comparison. I would compare NextCloud to the likes of Google Workspace + Photos, and with iCloud.

"With Nextcloud One, users have easy access and can share and collaborate on their files, photos and documents wherever they are. All that without any data leaks to third parties and having full control over their data."

I have access to a regular Nextcloud server. I can share files, edit Markdown documents and do basic image editing (cropping, rotating, resizing)

These are all things I can also do on Dropbox, Dropbox has a few more features here like the ability to add Microsoft Office and Google Docs/Sheets/etc documents.

What am I missing here? What can Nextcloud do that Dropbox can't?