I have tested several flatpak electron apps, including Signal, Slack, Freetube, all of them seems to give the following error:

ERROR: ld.so: object '/var/run/host/usr/lib64/libhardened_malloc.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored.

This error does not appear in app in other framework, like fsearch, syncthingy, or gnome core app. Native apps like codium and chormium also don't have this issue.

Example command:

flatpak run org.signal.Signal --filesystem=host-os:ro

My signal is running xwayland and slack is running in wayland, yet both of them raise the same error, so I don't think it is a wayland issue.

I don't know if this can be reproduced on other systems.

Deployment info (rpm-ostree status):

  ostree-image-signed:docker://ghcr.io/secureblue/silverblue-main-laptop-userns-hardened:latest
                   Digest: ...
                  Version: 39.20240130.0 (2024-01-30T18:19:08Z)
          LayeredPackages: ...
                Initramfs: regenerate

... represents unrelated information.