Message in every sketch

Good morning. On a win 11 64 bit computer, with version 2.3.10 installed and e win 8 compatibility mode (this was chosen between win 7, vista (sp 1 & 2), in every sketch, even in blink, I get this message:
In file included from C:\Users\admin\AppData\Local\arduino\sketches\8F2C993FF79AB91E3445855A847DDD55\sketch\Blink.ino.cpp.merged:1:0:
C:\Users\admin\AppData\Local\Arduino15\packages\arduino\hardware\avr\1.8.8\cores\arduino/Arduino.h:28:10: fatal error: avr/pgmspace.h: No such file or directory
#include <avr/pgmspace.h>
^~~~~~~~~~~~~~~~
compilation terminated.
exit status 1

Compilation error: exit status 1

I am not an expert, I enjoy arduino applications and any suggestion and / or help, will be welcome. I use uno and nano clones.
Thanks for your time.

My first suspicion would be an incorrect/incomplete AVR core installation. @ptillisch gives instructions for reinstalling the core here:

Dear Mr. van_der_decken,

thank you for your answer, but also for your time, I appreciate it. I followed your instructions faithfully and you solved the whole problem with complete success.

I am deeply indebted to you, because you gave an old pensioner the continuation of the joy of learning.

May God almighty bless you.

I am especially glad that I have been a humble student of a worthy teacher.

Thank you ! :folded_hands:

If you look below #post2 that was solved by @van_der_decken in 1 milli second you will see a small "Solution" icon , click on that to show there was a Solution.

Dear mr mikedb,
thank you very much for the suggestion.

Unfortunately, I was not aware of it and I apologize for my ignorance. I am an analog person and I live in a digital age. Thanks to everyone's suggestions, I'm trying to get better, even though I'm 65 and digitally illiterate. From my mistake, I gained experience and that was a success for me.

Thank you again for your wise suggestion, be well and be careful.

We all learn something new every day no matter our age.