[JavaScript Error: "Component returned failure code: 0x804b000a (NS_ERROR_MALFORMED_URI) [nsIIOService.newURI]" {file: "chrome://zotero/content/xpcom/storage/webdav.js" line: 205}]

Are there non-alphanumeric characters in your WebDAV URL, username, or password?

See this thread for how you can experiment to see what characters are causing this error, and let us know what you find:

https://forums.zotero.org/discussion/comment/419796/#Comment_419796

Same answer.