[solved] Can unused pin on SPI really be used for another purpose?

Maybe it should but in fact not.
Just connecting a Nokia5110 to the Pico.
SCK to pin B13
MOSI to B15
D/C to B10
RST to B1
SCE to B14 or A8
GND to GND
VCC to 3.3V

This code gives a blank screen

B14.write(1); //CS_LCD

var g;

var MONTHS = [
  "Jan","Feb","Mar","Apr","May","Jun",
  "Jul","Aug","Sep","Oct","Nov","Dec"
  ];

function draw() {
  g.clear();
  var t = new Date();
  var date = t.getDate()+" "+MONTHS[t.getMonth()]+" "+t.getFullYear();
  var time = t.getHours()+":" + 
       ("0"+t.getMinutes()).substr(-2);
  var secs = ("0"+t.getSeconds()).substr(-2);
  // top left date
  g.setFontBitmap();
  g.drawString(date,0,0);
  // middle time
  g.setFontVector(20);
  var timeWidth = g.stringWidth(time);
  g.drawString(time,(g.getWidth()-timeWidth-12)/2,10);
  // seconds over to the right
  g.setFontBitmap();
  g.drawString(secs,(g.getWidth()+timeWidth-8)/2,26);
  // send to LCD
  g.flip();
}

function onInit() {
  clearInterval();
  // Setup SPI
  //var spi = new SPI();
  SPI2.setup({ sck:B13, mosi:B15});
  // Initialise the LCD
  // connect(/*=SPI*/_spi, /*=PIN*/_dc, /*=PIN*/_ce, /*=PIN*/_rst, callback)
  g = require("PCD8544").connect(SPI2,B10,B14,B1, function() {
    // When it's initialised, set up an animation at 1fps (1s per frame)
    setInterval(draw, 1000);
  });
}

onInit();

and this one works as expected

A8.write(1); //CS_LCD

var g;

var MONTHS = [
  "Jan","Feb","Mar","Apr","May","Jun",
  "Jul","Aug","Sep","Oct","Nov","Dec"
  ];

function draw() {
  g.clear();
  var t = new Date();
  var date = t.getDate()+" "+MONTHS[t.getMonth()]+" "+t.getFullYear();
  var time = t.getHours()+":" + 
       ("0"+t.getMinutes()).substr(-2);
  var secs = ("0"+t.getSeconds()).substr(-2);
  // top left date
  g.setFontBitmap();
  g.drawString(date,0,0);
  // middle time
  g.setFontVector(20);
  var timeWidth = g.stringWidth(time);
  g.drawString(time,(g.getWidth()-timeWidth-12)/2,10);
  // seconds over to the right
  g.setFontBitmap();
  g.drawString(secs,(g.getWidth()+timeWidth-8)/2,26);
  // send to LCD
  g.flip();
}

function onInit() {
  clearInterval();
  // Setup SPI
  //var spi = new SPI();
  SPI2.setup({ sck:B13, mosi:B15});
  // Initialise the LCD
  // connect(/*=SPI*/_spi, /*=PIN*/_dc, /*=PIN*/_ce, /*=PIN*/_rst, callback)
  g = require("PCD8544").connect(SPI2,B10,A8,B1, function() {
    // When it's initialised, set up an animation at 1fps (1s per frame)
    setInterval(draw, 1000);
  });
}

onInit();

I have updated my Pico to 1V80