How to install flatpak-builder in rhel docker (ubi)?

For context: I'm trying to crossbuild wezterm-mux-server to use it on remote servers of my company that run RHEL 9.2+. Since I don't have full root access I want to crossbuild them on my local machine and then copy over the binaries. The problem is that the build needs some distro-related dependencies, e.g. for rhel it needs flatpak-builder. Now how do I get flatpak-builder into the rhel docker image (ubi)? It doesn't seem to be included in any of the upstream repos that is queried by yum. Here are my steps so far: Pull and execut docker image: docker login registry.redhat.io # Use your red hat usename and password docker pull registry.redhat.io/ubi9/ubi:9.5-1732804088 docker run -v $PWD:/opt -it --entrypoint /bin/bash registry.redhat.io/ubi9/ubi:9.5-1732804088 From within the image execute: yum install flatpak-builder Which results in the following error message [root@00cef48d6bb3 /]# yum install flatpak-builder Updating Subscription Management repositories. Unable to read consumer identity This system is not registered with an entitlement server. You can use subscription-manager to register. Red Hat Universal Base Image 9 (RPMs) - BaseOS 1.4 MB/s | 525 kB 00:00 Red Hat Universal Base Image 9 (RPMs) - AppStream 461 kB/s | 2.3 MB 00:05 Red Hat Universal Base Image 9 (RPMs) - CodeReady Builder 1.0 MB/s | 281 kB 00:00 No match for argument: flatpak-builder Error: Unable to find a match: flatpak-builder Building from source is not really an option since flatpak-builder itself needs a ton of additional dependencies (I don't want to build the whole dependency tree manually). So my prefered way is to do it with a package manager. However since I'm a newbie to RHEL I have no idea how to add a new online repository or how to find out which online repositories even contain flatpak-builder?