Ubuntu has announced support for The PolarFire SoC FPGA Icicle Kit RISC-V Board. I am not always a huge fan of Ubuntu but if you're looking to get into RISC-V boards they seem to be always on the forefront of support. RISC-V is a great platform to get into as many boards have an open source BIOS and the architecture as a whole is a lot more open than x86.

The board can be found on Mouser among other stores.

https://www.mouser.ca/new/microchip/microchip-polarfire-soc-icicle-kit