I tried installing Stockfish 15 files I made available on version .9l of Picochess and it definitely does not work. I got the same err.engine messages others were seeing. So, the SF15 files only work on version 3 of Pico as far as I know.
How to load Stockfish 15 on DGT Pi 3000

aha. I really don't get it.
No way I can find the files. Links are looking in my own Onedrive, not finding it.
There must be a normal link to the image yes?

Your DGT Pi is running Raspberry Pi which is a Linux operating system
You have to access the Linux operating system from your PC using Powershell or login into your DGT Pi through the terminal. login id: 'pi', password: 'picochess'
For the Powershell login...
1) Enable OpenSSH on Windows
2) Find you IP address of your DGT Pi
3) Login to the Linux OS through Powershell
ssh pi@192.168.1.xx
password picochess
4) You place the files in /opt/picochess/engines/aarch64/
5) Set the Stockfish file to executable
They did an awesome job., a really awesome job!! The speech portion is so much clearer, and the tutor/coach is not annoying at all in my opinion. Should be a fun evening this evening as I try some of the other modes I observed.
ordering the Elecrow 10.1 Inch Raspberry Pi Screen 1920X1080p HDMI VGA Portable Monitor from amazon the non-touchscreen as you recommended