qemu-system-avr tries to use all the CPU cicles (leaving a CPU core stuck at 100%; limit CPU core usage to 10% via --cpus 0.1. It can be adjusted on slower machines.
$ podman build -t dcc/net-to-serial:sim .
$ podman run --init --cpus 0.1 -d -p 2560:2560 dcc/net-to-serial:sim