Edit the file administrator/components/com_akeeba/BackupPlatform/Joomla3x/Platform.php and find this block of code in lines 735-751:

	// If the release is older than 3 months, issue a warning
	if (defined('AKEEBA_DATE'))
	{
		$releaseDate = new Date(AKEEBA_DATE);

		if (time() - $releaseDate->toUnix() > 10368000)
		{
			if (!isset($ret['warnings']))
			{
				$ret['warnings'] = [];
				$ret['warnings'] = array_merge($ret['warnings'], [
					'Your version of Akeeba Backup is more than 120 days old and most likely already out of date. Please check if a newer version is published and install it.',
				]);
			}
		}

	}

Change the second line reading if (defined('AKEEBA_DATE')) to now read:

if (false) Save the file. Now the code which was adding the backup warning is removed.

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