To me it still seems that this display cannot receive image data through SPI bus.
On the waveshare site itself, when clicking on certain display product page, you can usually find a table named Selection guide. In that table waveshare has listed and explicitely divided displays to:
smaller displays that are driven through GPIO using SPI bus to write graphics data and the same SPI bus to read touch data,
bigger displays (above 4inch) are using HDMI as data bus for graphics and SPI bus for touch data.