so, I set up uppy on the frontend and integrated uppy-server into an existing express app. however I can’t seem to figure out what URL to use to upload to uppy-server. I’m sure I’m missing s.th. obvious here.
It seems you are trying to upload your files directly to uppy-server. This is not what uppy-server is built for.
The purpose of uppy-server is to help you import remote files from known providers, e.g Dropbox, Instagram, GoogleDrive, and then upload them to your target server. Uppy-server itself does not serve as a target upload server.
I had the same misunderstanding. Would that mean if wanted to implement Uppy client for standard file upload (from client device) I would need to also implement a Tus server?
you need to be running a tus server somewhere yes, but you don’t have to implement it yourself. There are existing implementations you can run standalone. See https://github.com/tus/tusd/releases/