Is this normal?
Joplin does run Electron, which is a bunch of Chromium and node.js engine changes. It is bigger than a typical native application.
Please also keep in mind that each plugin also adds an additional process that uses quite a bit of memory.
I always thought Microsoft apps are huge and I'm surprised that OneNote uses so little memory--but maybe it shares some memory with Windows.
my is 15 parts 540 MB, so yes, yours doesn't appear abnormal.