You need to install dbus-glib.
Icecat is missing all of the automatically generated dependencies:
$ rpm -q --requires icecat
/usr/bin/bash
dconf
fedora-bookmarks
mozilla-filesystem
nspr >= 4.32
nss >= 3.88
p11-kit-trust
rpmlib(BuiltinLuaScripts) <= 4.2.2-1
rpmlib(CompressedFileNames) <= 3.0.4-1
rpmlib(FileDigests) <= 4.6.0-1
rpmlib(PayloadFilesHavePrefix) <= 4.0-1
rpmlib(PayloadIsZstd) <= 5.4.18-1
It probably needs something similar to PR#27: Make provides/requires filtering smarter/automatic - rpms/firefox - src.fedoraproject.org
Please file a bug against icecat.