Canonical has been releasing Ubuntu RISC-V images for SBCs and QEMU at least since 2021. The latest addition is an Ubuntu 24.04 Server image for the Mars credit-card-size SBC powered by StarFive JH7110 quad-core RISC-V SoC and designed by Shenzhen Milk-V Technology.
That means we now have Ubuntu Server images for the QEMU emulator, AllWinner Nezha SBC, Microchip Polarfire SoC FPGA Icicle Kit, SiFive Unmatched mini-ITX motherboard, Sipeed LicheeRV Dock, StarFive VisionFive 2 SBC, and the Mars SBC. You’ll note there aren’t any Ubuntu Desktop images for now, because the GPU (if any) in RISC-V SoCs is not yet fully supported.