Exactly what @odolvlobo said. But in case you don't know whether your Ubuntu is 32-bit or 64-bit, you could check it by either checking filename of Ubuntu ISO you download or running command uname -a. If your Ubuntu is 64-bit, you should able to see keyword "64-bit", "arm64", "aarch64" or "armv8".
You mean not all recent-gen Raspberry Pis run arm64 OSes?
The full-sized Raspberry Pis are 64-bit and I'm pretty sure you can't even install 32-bit Linux on a 64-bit ARM chip. Meanwhile it should be possible to do so by mistake on x86.
Thanks everybody! ...just 11 years of sync to go
Kit: Rapsberry Pi 4 (8GB Ram), running Ubuntu latest version with an external ssd ready to go.
With 8GB of RAM and external SSD, it should go fairly quickly. In my experience on low-end x86 hardware, with good memory setup like yours, it took only a couple days.
Memory upgrade from 4GB to 8GB happened where you see the curve go straight up! Good on you that you were able to snatch an 8GB Pi.