As reported upstream (https://github.com/FedoraQt/MediaWriter/issues/217): the application doesn't write anything to the disk, even though it says "writing".
Opening this bug for the purpose of the Fedora Prioritized Bugs process.
In today's meeting, we agreed to accept this as a prioritized bug:
Martin, do you have an update on the Catalina support possibilities we discussed in the last Prioritized Bugs meeting?
I will try to look into that. I'm currently waiting for a hardware and then I guess it will take a while until I find out as I have never used MacOS before.
Update: I have a MacBook and I started working on it.
We have a working solution, which is currently on review here → https://github.com/FedoraQt/MediaWriter/pull/256. I think or hope we can have a release soon.