Sadly that’s a known issue per Native "program" command does not work · Issue #11 · kendryte/openocd-kendryte · GitHub.
However it also says that a GDB load command works. This might mean that debugging works and for normal firmware uploading you should use the old upload method.
Try
[env:sipeed-maix-bit]
platform = kendryte210
board = sipeed-maix-bit
framework = kendryte-standalone-sdk
monitor_speed = 115200
board_build.mcu = K210
; change MCU frequency
board_build.f_cpu = 400000000L
; uplaod via OpenOCD does not work.
upload_protocol = kflash
; debug.. (which includes a firmware upload but through a different method) maybe.
debug_tool = sipeed-rv-debugger
Try going into the debugger sidebar and press the play button. (of course selecting the correct project env and debugger config corresponding to the project are prerequisites).