This is what worked for me on the Librem 5 with Byzantium:
I followed the steps to install Anki via PyPI/pip (mentioned by @FranklyFlawless above), but had to adjust them a bit. So this is what I did:
Install the PyQt5 packages:
sudo apt install python3-pyqt5.{qtwebengine,qtmultimedia}
Create a directory for Anki and cd into that directory:
mkdir anki
cd anki
Then run the following:
python3 -m venv --system-site-packages pyenv
pyenv/bin/pip install --upgrade pip
pyenv/bin/pip install --upgrade --pre aqt
Start Anki:
QT_QPA_PLATFORM=wayland pyenv/bin/anki