Comment 9 for bug 1850977

snapd asks polkit for the authorization, looking at the log, pokit belives the user is an admin:

ov 05 15:15:46 jms-u18t polkitd(authority=local)[881]: Operator of unix-session:116 successfully authenticated as unix-user:jason to gain TEMPORARY authorization for action io.snapcraft.snapd.manage for unix-process:18050:34595600 [snap install blender] (owned by unix-user:jason)

The policy is defined as follows:

  <action id="io.snapcraft.snapd.manage">
    <description gettext-domain="snappy">Install, update, or remove packages</description>
    <message gettext-domain="snappy">Authentication is required to install, update, or remove packages</message>
    <defaults>
      <allow_any>auth_admin</allow_any>
      <allow_inactive>auth_admin</allow_inactive>
      <allow_active>auth_admin_keep</allow_active>
    </defaults>
  </action>

According to the manual auth_admin means 'Authentication by an administrative user is required'. Any clue why polkit might belive you are an admin user? Perhaps the local policy was tweaked to allow this?