"Downgrades to a previous major release are not permitted" message when upgrading to cPanel version 100

Symptoms

When upgrading to cPanel version 100 from a version before 76, cPanel will not upgrade and gives output similar to:

=> Log opened from /usr/local/cpanel/scripts/updatenow (4139) at Fri Nov 12 23:51:09 2021 
[2021-11-12 23:51:09 +0800] Detected version '11.70.0.69' from version file. 
[2021-11-12 23:51:09 +0800] Running version '11.70.0.69' of updatenow. 
[2021-11-12 23:51:09 +0800] Target version set to '11.100.0.2' 
[2021-11-12 23:51:09 +0800] E Blocker found: Downgrades to a previous major release are not permitted. 
[2021-11-12 23:51:09 +0800] W An attempt to up/downgrade to 11.100.0.2 was blocked. Please review blockers. 
[2021-11-12 23:51:09 +0800] E The install encountered a fatal error: An attempt to up/downgrade to 11.100.0.2 was blocked. Please review blockers. 
=> Log closed Fri Nov 12 23:51:09 2021

Description 

Older versions of cPanel do not recognize three-digit version numbers and attempt to downgrade to version 10 instead of upgrading to version 100.

We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-39256. Follow this article to receive an email notification when a solution is published in the product.

Workaround

Set the release tier to '11.76,' then proceed with the upgrade. Once cPanel has been upgraded to version 76, the release tier may be set to any branch you'd like to use moving forward. The steps below detail how to do this.

1. Access the server's command line as the 'root' user via SSH or "Terminal" in WHM.
2. Open the /etc/cpupdate.conf file in your preferred text editor.
3. Change the CPANEL line to the following:
   

   CPANEL=11.76

4. Save the changes and exit the text editor.
5. Update cPanel.

   /scripts/upcp

6. Open the /etc/cpupdate.conf file in your preferred text editor.
7. Change the release tier to your desired release tier.
8. Save the changes and exit the text editor.
9. Update cPanel again.

   /scripts/upcp

Additional resources

How to edit a file on command-line

How to change the cPanel release TIER on your server