after installed nextcloud 15.0.0,it work ok in Web browser,but when use windows app,it seems some thing wrong,it Promptes" Server Internal Error"
Can you check if you have the same issue like this user:
https://github.com/nextcloud/desktop/issues/718 (with or without slash at the end)
If the use of the slash is so important, we probably have to check your configuration and compare to others.