Last tag is 1.8.1, we are shipping 1.8.0. https://github.com/flatpak/xdg-desktop-portal/tags I'm not sure if it fixes anything specifically, but I'm chasing after a bug that makes screen sharing not work through the portal, having the last stable release could help to cross some ts.
I'm also unable to build a different version because libportal-dev is not available :/ Rebuilding xdg-desktop-portal on 1.8.1 (and libportal, of course) fixed screen sharing on portals. Falling back to 1.8.0 also fixed it for me, so we'd need to make sure packaging is on point. Making sure we build against newer libportal would make sense (?). I've not been able to reproduce the failure by building xdg-desktop-portals myself. An easy way to test if it's working is by "flatpak install com.obsproject.Studio", running it and adding a screen sharing source.
This was a packaging bug fixed here: https://bugs.launchpad.net/ubuntu/+source/xdg-desktop-portal/+bug/1879580 We just need to update the Neon packaging.