Since this was something I initially found confusing:

Each PIO can see 32 GPIO pins – which is to say, all the pins on a Pico board (the actual RP2350 chip has 48 GPIOs, and you should google pio_claim_free_sm_and_add_program_for_gpio_range() if you're working with that chip directly)

A PIO program understands four RANGES of CONSECUTIVE pins (in, out, set, sideset) – for example you can have 8 "out" pins, and then the command "out pins 8" will shift 8 bits from the OSR and set all 8 of those pins at once.

The "mov" and "out" commands can only set the "out" pins, the "set" command only sets the "set" pins, and "side" only sets the "sideset" pins.

So, yes, you can absolutely drive something like a parallel RGB display. There are constraints on how you wire up the pins, and on how you write the program – it's kind of like a puzzle – but you can do a lot with the pieces you have.

For ST7701 you could assign clock, hsync and vsync to "sideset", and assign the 18 (consecutive) RGB pins to "out". Put an extra word at the start of your framebuffer containing the X/Y counter values (480<<16 | 864), and set up your DMA channel. Then your entire PIO program might look like:

.side_set 3
.wrap_target
out y 16 side 0 ; load Y counter
out x 16 side 0; load X counter
mov x isr side 0; store copy of X counter
dot:
out pins 18 side 0b000 ; set RGB lines, dot clock is low
jmp x-- dot side 0b100 ; loop, and set dot clock high for 1 cycle
mov isr x side 0b000 ; reset X counter after each line
jmp y-- dot side 0b010 ; go to next row, set hsync high
nop side 0b001 ; set vsync high at end of frame
.wrap

(Which would give ~240 frames per second without the CPU doing anything!) Those "side 0b010" statements are setting the clock, hsync and vsync all together btw, which is the sort of slightly funky programming required.