Probably it is a little bit easier. Just let the updater run with php7.2 (if it is installed) instead of downgrading the whole NC-instance as mentioned in another topic: Update to 20.0.9 instead of 21.0.1
I dit this and it worked fine on my side:
php7.2 updater.phar
Nextcloud Updater - version: v20.0.0beta4-11-g68fa0d4Current version is 20.0.8.
Update to Nextcloud 20.0.9 available. (channel: “stable”)
Following file will be downloaded automatically: https://download.nextcloud.com/server/releases/nextcloud-20.0.9.zip
Open changelogSteps that will be executed:
Check for expected files
Check for write permissions
Create backup
Downloading
Verify integrity
Extracting
Enable maintenance mode
Replace entry points
Delete old files
Move new files in place
DoneStart update? [y/N] y
Info: Pressing Ctrl-C will finish the currently running step and then stops the updater.
[
] Check for expected files
[] Check for write permissions
[] Create backup
[] Downloading
[] Verify integrity
[] Extracting
[] Enable maintenance mode
[] Replace entry points
[] Delete old files
[] Move new files in place
[] Done
Update of code successful.
Should the “occ upgrade” command be executed? [Y/n]
Nextcloud or one of the apps require upgrade - only a limited number of commands are available
You may use your browser or the occ upgrade command to do the upgrade
[…]
Keep maintenance mode active? [y/N]
Maintenance mode disabledMaintenance mode is disabled