After entering the domain of the Nextcloud 24 installation in the Android Nextcloud Client on a Android 5 Tablet, it is possible to click on “Login” to get this new device authentificated but afterwards a blue Nextcloud page appears and no login/password fields show up. So no usage of the Android Nextcloud Client is possible.
Via Chromium on the same device it is possible to see the login/password fields and it is possible to login in and see the files. On Firefox & Iceweasel the same problem as with the Android Nextcloud Client - only a blue screen, no possibility to enter the account data nor login…
To access a Nextcloud 20 or 22 server with the same Android 5 Tablet and the same Nextcloud Client is no problem.
As far as i know, the Nextckoud Android app requires at least API level 23 (which matches Android 6).
While you can of course use older versions, they won’t support new features or receive bug fixes, it is absolutely possible in my opinion that they do not necessarily work with newer Nextcloud versions.
One could argue whether this is an issue that should be fixed (or not happen at all) even though it is no5 supported, but on the other hand - it’s not supported