I was able to deploy MikroTik CHR on Hetzner just this last month actually without issues with booting during the CHR install itself.
In my case, the CHR runs in CentOS 8 Stream as KVM Guest on a Hetzner dedicated machine (with two WAN IP's - one for the dedicated server, other for the CHR and network behind it) with AMD Ryzen 5 3600 CPU. Currently enjoying the benefits of the recently added ZeroTier One functionality actually.
Maybe the official guide works for VirtualBox, but it never worked for me on Qemu/KVM, what I did was the following:
[*] Download the CHR Raw disk image from:
https://mikrotik.com/download
[*] Extract the archive
[*] Convert the IMG to QCOW2 format
[*] Resize the disk image to expand it's size (best to do it initially, so that CHR automatically extends the system partition to all available disk space and you don't have to resize it later)
wget https://download.mikrotik.com/routeros/7.1/chr-7.1.img.zip
unzip chr-7.1.img.zip
qemu-img convert -f raw -O qcow2 ./chr-7.1.img ./chr-7.1.qcow2
qemu-img resize ./chr-7.1.qcow2 +10G
And even tho, the latest CHR versions are suppose to be EFI compatible, I still used Legacy BIOS boot for VM config - EFI was never supported in any CHR 6.x version apart from Development/Testing channels. When running directly in the cloud, writing it directly to the disk might require setting up the boot flag too.