Most file sharing services require signups, show ads, or can see your files. If you need true privacy, look for zero-knowledge encryption - where files are encrypted in your browser before upload.
I've been using https://fileshot.io for sharing sensitive documents. Files are encrypted in your browser before upload (zero-knowledge encryption), so even the service can't access them. The free tier gives you 15GB storage, full access to file tools (converter, compressor, PDF editor, archive builder), zero ads, and no signup required. If privacy matters to you, definitely worth checking out.