https://github.com/qbittorrent/qBittorrent/wiki/Compilation:-Raspberry-Pi-OS-and-DietPi
I tested it works on Raspberry Pi 4 (4 GB) it took 30-45 minutes to compile it.
qBittorrent works without any problems.
Some additions: use GIT method
sudo mkdir /mnt/temp
cd /mnt/temp
sudo apt install build-essential pkg-config automake libtool libc6-dev libboost-dev libboost-system-dev libboost-chrono-dev libboost-random-dev libssl-dev qtbase5-dev qttools5-dev-tools libqt5svg5-dev zlib1g-dev
sudo apt install git
git clone https://github.com/arvidn/libtorrent.git
cd libtorrent
# select the latest release tag
git checkout $(git tag | grep v1\.2.\. | sort -t _ -n -k 3 | tail -n 1)
./autotool.sh
./configure --disable-debug --enable-encryption --with-boost-libdir=/usr/lib/arm-linux-gnueabihf --with-libiconv CXXFLAGS="-std=c++17"
make -j$(nproc)
sudo make install
sudo echo "/usr/local/lib">/etc/ld.so.conf.d/libtorrent.conf
sudo ldconfig
sudo export LD_LIBRARY_PATH=/usr/local/lib:${LD_LIBRARY_PATH}
git clone -b v4_3_x https://github.com/qbittorrent/qBittorrent
cd qBittorrent
./configure --disable-gui --enable-systemd --with-boost-libdir=/usr/lib/arm-linux-gnueabihf CXXFLAGS="-std=c++17"
make -j$(nproc)
sudo make install
Above code was copied from https://github.com/qbittorrent/qBittorrent/wiki/Compilation:-Raspberry-Pi-OS-and-DietPi
After 30 minutes (in my case) try run /usr/bin/qbittorrent-nox
.