The biggest difference is probably the desktop UI. After that Ubuntu has a bit more of a unified experience. Part of that is because Ubuntu tends to make a lot more decisions for you, whereas Debian gives you more options upfront. There is a nice integrated GUI(I know Debian has one but its less integrated) for installing packages. Online resources tend to discuss Ubuntu specifically due to its larger market share on the desktop. There is the Ubuntu PPA(Personal Packaged Archives) which don't always work easily in Debian.
They are both fairly similar internally. I have been a long term Debian user(decades), and I never feel out of place working with Ubuntu. That is not always the case when I'm working with Red Hat or Arch or some other distributions. Debian probably requires a bit more fiddling and a bit more general Linux and computing knowledge, but if you have been using Linux for a bit, I think you would be just fine.
They are both fairly similar internally. I have been a long term Debian user(decades), and I never feel out of place working with Ubuntu. That is not always the case when I'm working with Red Hat or Arch or some other distributions. Debian probably requires a bit more fiddling and a bit more general Linux and computing knowledge, but if you have been using Linux for a bit, I think you would be just fine.