There is now a nightly flatpak of KMyMoney available. You can install it with:
flatpak install -u https://cdn.kde.org/flatpak/kmymoney-nightly/org.kde.kmymoney.flatpakref
or to only add the repository:
flatpak remote-add -u kmymoney-nightly https://cdn.kde.org/flatpak/kmymoney-nightly/kmymoney-nightly.flatpakrepo
It is built from the current development version, so there’s a possibility of more bugs, but you will also get bugfixes faster than the stable version.