To give one simple example, any app using the go language, where we take the release builds, has to get some logic or separate Dockerfile to deal with arm.
I have some experience with this and have set up my own multi-arch go build pipelines using a single Dockerfile for some of my other apps: minitor-go, dockron, tag-checker, and for Python ones too: original minitor.
Here's a sample repo demonstrating my process: multiarch-pipeline-test. It's easier these days if your server has docker buildx though.
Also, since with Cloudron we're most often building things that exist upstream, here's an example multi-arch build repo I have for the Golang project cadvisor. It will auto build a particular cadvisor version on a git tag so I just need to create a release on my Gitea server and the build is started and deployed. With cadvisor, I have to clone the whole repo and cross-compile the cadvisor binary for arm becaue there is no pre-compiled binary. If there is, it should be even easier to just pull that binary.
Anyway, I'm happy to help if there are any applications that may be critical to be ported.