If you’re really new to Linux I’d recommend you run an Ubuntu VM and not Debian. Debian normally doesn’t update as fast and is normally a smaller/lighter load. This is whats causing your issue here. If you start with an “easier” Linux flavor you’ll have an easier learning curve. I have installed on Ubuntu 22.04 and the umbrel.sh works flawless.
Curl is not part of Umbrel application set.
As per Google: cURL is a computer software project providing a library and command-line tool for transferring data using various network protocols.
People who are using linux, usually have an idea about curl. Please do not blame install instructions without understanding it correctly.
You just need to install curl 1st in order to make this work. If you’re jumping into Linux I’d highly recommend getting good at Google searches for how-tos on each issue you come across. As an example:
Googling “install curl on ubuntu” leads you to the following: