I changed my boot switches to SDIO (to read the latest firmware from the MicroSD card) and booted with the latest 202306 image (which included u-boot-spl.bin.normal.out and visionfive2_fw_payload.img on the first two partitions)
And then used these commands to upgrade the onboard QSPI NOR FLASH:
And because I booted with the latest image there was absolutely zero chance of an older dtb (device tree binary) with a smaller first partition truncating my firmware. The first partition on the QSPI NOR FLASH was changed from 128 KiB to 256KiB in the later dtb’s of the newer disk image files.