Joplin version: 2.9.2
OS specifics: Windows 10
I met exactly the same bug as this closed one
I'm not the original poster of this issue and I don't know if I should create a new issue in Github. But I think post something there is necessary.
In short, if Joplin is set to use a proxy, then it will fail to fetch the resource and reports "url.startsWith is not a function".