Plesk Backup Manager doesn't work when Seafile is installed on AlmaLinux: PleskPMMResponseException

Symptoms

• Plesk is running on AlmaLinux, and Seafile is installed

• Backup Manager returns error 500:

  Type PleskPMMResponseException
  Message Failed to parse response. Reason: Failed to read data from stream Process output: 
  File PMMConnector.php 
  Line 795

Cause

Seafile installed Python 3.9, which isn't compatible with Plesk.

Resolution

Remove the link to Python 3.9 and link a compatible version.

1. Log in over SSH

2. Symlink Python 3.6 as the default Python binary:

   # mv /usr/bin/python3{.bak} && ln -s /usr/bin/python3.6 /usr/bin/python3