How to stop qbittorrent continuing to seed after whatever ratio limit that you want has been reached:
Open the client settings: Select the BitTorrent panel: In Share Ratio Limiting check the box "[ ] Seed torrents until their ratio reaches; Set the value; Choose the action from Pause them | Remove them
Press OK to close the client.
If you do not want to seed at all after downloading, set the value to 0. Please note this goes against the basic principles of using a Bittorrent client, but is of course your personal preference.
Please note if you are using a ratio enforcing 'private' tracker, the ratio shown in the client, is not the same ratio as your tracker is reporting or monitoring.