kio-5.63 makes kdav-19.08.2 fail with HTTP error (400) STEPS TO REPRODUCE Install the mentioned packages. Try to connect to a davical server via https. RESULT HTTP error (400). Works with kio-5.62. Reverting commit 9713ea02e49eda11d72e1ac605417dac0dab8c37 "Consider the usage of WebDAV methods sufficient for assuming WebDAV" in kio-5.63 makes kdav work again.
This has been fixed in https://phabricator.kde.org/D24880 for 5.64. Any chance you can test that the fix works for you?
Yes, I can confirm this fixes this problem. Thanks!