TRINKET M0 - no Device info - no header files error

I am a real beginner, I watched a LOT of tutorials on arduino and Trinket M0, also involved a friend, a software engineer, even if not well trained on Arduino, but after 3 weeks no solutions.

First of all, in not clear YET, which board model I should chose from the list (Trinket M0 or Arduino Uno).
Is not clear wich PROGRAMMER (AVR ISP? USB tiny ISP?? USB ASP.... ??)
I tried several combination with same result :
Not able to see board type, what I get is:

BN: Unknown board
VID: 239A
PID: 801F
SN: Upload any sketch to obtain it

NO HEADER FILES error with any sketch I try to send , also with the one you get when you open arduino, this one:

void setup() {
** // put your setup code here, to run once:**
void loop() {
** // put your main code here, to run repeatedly:**

or the BLINK one... with any ketch.

Error I get is Always:

Invalid library found in C:\Users\nolli.GMM-BG\AppData\Local\Arduino15\packages\adafruit\hardware\samd\1.2.9\libraries\strandtest: no headers files (.h) found in C:\Users\nolli.GMM-BG\AppData\Local\Arduino15\packages\adafruit\hardware\samd\1.2.9\libraries\strandtest

I am desperate!!

Nick from ITALY