Rather than start a new thread I'm posting here because I too am having trouble getting Nextcloud (free shared hosting provide setup via Nextcloud's website) setup
The attachments show the app password from nextcloud and my attempt to enter that info into KOReader. I copied the login details and pasted into Notepadd++ then into the reader settingslua on my KOReader to avoid typos.
The error message in the crash log is
WARN Error fetching existing notes from Nextcloud Server HTTP response code is not OK
I tried modifying the URL to
https://tio.lv.tab.digital/apps
but that made no difference to the result. What am I doing wrong