As written in the official issue ticket, following the way how to solve your conflict locally.
A quick update to figure out the conflicted files.
cd into your nextcloud synchronized path
#list conflicted files
find . -iname *conflic* -type f
You can than decide which file is the one you want to keep foo.bar or foo (conflicted copy 2020-09-09 083407).bar.
So, nextcloud version 15.0.x is out already and whenever you are logging into your next cloud with your administrator account, you still get this "you are on the latest version" message.
Further more, you just got a update to version 14.0.x while waiting for version 15.0.x.
To fix this, all you have to do is to switch from the channel "stable" to "beta". After a page reload, you should see a version 15.0.x available. Do the upgrade and do not forget to switch back to the stable channel.
I am doing all via the command line. I've a separate data directory (not included below public/data).
Here are my simple steps (database backup not included). I did the upgrade from the latest 12 release. This is a KISS tutorial.
cd <root path>
wget "https://download.nextcloud.com/server/releases/nextcloud-13.0.0.zip"
unzip nextcloud-13.0.0.zip
mv public public_12_0_5
mv nextcloud public
cp public_12_0_5/config/config.php public/config/config.php
rsync -rv --dry-run public_12_0_5/apps public/apps
#if needed
#rsync -rv public_12_0_5/apps public/apps
Good luck on your side.
Currently, I've found one issue with my news application.
I needed to execute following SQL statement:
UPDATE oc_jobs SET reserved_at = 0 WHERE (argument = '["OCA\\News\\Cron\\Updater","run"]' OR class = 'OCA\\News\\Cron\\Updater');
Thanks to the how to fix it section.
I don't thing nextcloud 12 is the issue here. Simple the old used "caldav" application and the connected AndroidCaldavSyncAdapater is not working anymore. I've removed the users everywhere as well as the application. I've switched the phone to use the DAVDroid installable via F-Droid.
The setup is so easy I won't write a howto section here.
Just be fair and donate some money to DAVDroid since the application is working out of the box.