How do you login to the web client usually? Via browser extension?

To do it via a web client (like primal, coracle, etc) you would have to add your umbrel relay to your relay list, but that means you also have to expose your relay to the internet (nat/portforward on your router) and then either use the public ip or setup some domain.

So your goal is to just have a private copy of your notes or for others to see them as well?