Milk-V Duo has been a pretty popular RISC-V board, one of the more mainstream affordable RISC-V boards. We did a reading group on RISC-V machine code where we used this as the initial board. It even has it's own fcked up vector instructions that are based an RVV draft with some extensions. gcc has its own arch specifier for it (xtheadvector*, e.g. -march=rv64gc_xtheadvector).