noarch packages shouldn't depend on specific architectures.
%package exporter
Summary: Prometheus exporter for Knot DNS
BuildArch: noarch
-Requires: %{name}-libs%{?_isa} = %{version}-%{release}
+Requires: %{name}-libs = %{version}-%{release}
%description exporter
The package provides Python Prometheus exporter for Knot DNS.
%package -n python3-libknot
Summary: Python bindings for libknot
BuildArch: noarch
-Requires: %{name}-libs%{?_isa} = %{version}-%{release}
+Requires: %{name}-libs = %{version}-%{release}
%{?python_provide:%python_provide python3-libknot}
%description -n python3-libknot