KyPass 4 supports WebDAV so it was worth a try.
Start KyPass 4 on your iOS device. Tap the cloud button.
Tick the option slider “Use WebDAV”
Enter your WebDAV URL and the credentials to login.
Are you using NextCloud/OwnCloud? In this case the URL should look like:
The folder must contain a kdb or kdbx file. KyPass 4 will display those files and you’re able to select one to open.
Close and restart KyPass 4. You’ll see your KeePass database and you’re good to go.