When is version 18 going to be available in the stable channel?
So far it only shows 17.0.8
In the Beta channel it used to be available, now it shows Nextcloud 17.0.9 RC1
What is going on?
I think it takes into consideration your php version. You need at least php 7.2 (https://docs.nextcloud.com/server/18/admin_manual/installation/source_installation.html#prerequisites-for-manual-installation)
The php version is 7.3
Use the stable channel. Update to the latest 17.0.x version, then it should suggest NC 18.