When you are asked to set a server (opening nextcloud app on android), it’s enough to enter murena.io. Then you will asked for your user and password. (found here:: https://community.e.foundation/t/how-to-sync-nextcloud-notes-with-murena-io/47079)
A problem, if you connect your android device with KDEConnect and you copy your password from your PC, could be to paste it in password field. For security reason your keyboard could not allow you to paste easy. But eventually I managed to paste it without typing it.