I thought with the Pico & Pi being made by the same company people on the RPi site would be using RPi gear to develop software for Pico on Pi400 but not using Pascal I guess.
Any error messages with the old 2021 Pi400 OS are irrelevant since FPCupdeluxe does nothing with the latest Pi software Bullseye issued April 2022 & instructions say update first. Someone needs to test FPCupdeluxe on the latest Pi software is my point or state it doesn't work on a Pi. I wouldn't know where to start.
Yeah sure. "You thought". And on the basis of that, without considering that you might be mistaken, you started off your first post with a slew of snarky comments :-(
Now let's put all that behind us and start over.
As I understand it, the Pi400 is basically a fairly standard Pi 4 running a derivative of Debian (I forget what they call it these days). I've been running RPis for... quite a long time, and by and large they behave much like PCs running Debian: or SPARCs, MIPS boards, emulated IBM mainframes and so on.
The Pico on the other hand, is- and just about every published piece over the last 18 months has emphasised this- a standalone board with no operating system, roughly speaking competing with the Arduino, "Blue Pill", Teensy and so on. So assuming that just because the Pico and the Pi400 are made by the same people they behave the same, is like assuming that an IBM PC and an IBM mainframe behave the same. Or that a Volvo car and a Volvo lorry behave the same or... I think you probably get the idea :-)
The only time I've used FPCUpdeluxe is for the Pico, and that was because I was following up work that other people had been discussing on this forum; however my understanding is that it's well-regarded and that I'm one of comparatively few people who, out of habit, builds FPC etc. using his own scripts.
Right now, I'm not diving in to look at how you should have set it up, and suggest that you listen to DonAlfredo.
MarkMLl