Related to When do German borders reopen for EU members exactly? but not this questions is specific to quarantine requirements.
What are the quarantine requirements for a German citizen entering Germany from outside the EU?
At the moment there appears to be a 14-day quarantine requirement but that appears to be up to the states. https://www.auswaertiges-amt.de/en/einreiseundaufenthalt/coronavirus
Does this change with the June 15 updates ?