I expect that on SFOS 3.3.0.x, install should be clean and there are no conflicts with Jolla's json-glib. I hope it will automatically uninstall json-glib from my repo when you update Flatpak, but haven't tested it.
The following packages have to be installed: flatpak-1.6.3.0-1.23.4.jolla.armv7hl Application deployment framework for desktop apps flatpak-runner-0.8.5-1.35.2.jolla.armv7hl Flatpak runner flatpak-session-helper-1.6.3.0-1.23.4.jolla.armv7hl User D-Bus service used by flatpak and others libappstream-glib-0.7.15.1-1.14.1.jolla.armv7hl Library for AppStream metadata ostree-libs-2019.6-1.14.2.jolla.armv7hl Development headers for ostree xdg-dbus-proxy-0.1.2-1.5.2.jolla.armv7hl Filtering proxy for D-Bus connections xdg-desktop-portal-1.4.2-1.10.8.jolla.armv7hl Portal frontend service to flatpak Proceed with changes? [N/y] y Updating packages Downloading packages Installing packages Finished [nemo@Sailfish ~]$ devel-su pkcon search libjson-glib Password: Searching by details Querying Finished Installed libjson-glib-1.4.4-1.2.1.jolla.armv7hl (installed) Library for JavaScript Object Notation format [nemo@Sailfish ~]$