Sometimes the "limit" isn't a setting, but a physical or logical boundary of your hardware.
Under Tools > Options > BitTorrent , there is a "Maximum active downloads" setting. If you exceed this number, new torrents will remain "Queued" and won't start until others finish. qbittorrent exceeded download limit
The most frequent reasons for this error are internal settings designed to manage bandwidth or prevent system instability. Sometimes the "limit" isn't a setting, but a