I built the esp32 blink demo project without errors using this:
"How to disable the Unresolved Symbol error markers" from here:
https://github.com/espressif/idf-eclipse-plugin/blob/master/FAQ.md#how-to-configure-esp-who-in-espressif-ide
And more:
- recommended here: by wtamayo » Wed Jan 10, 2024 5 ...

It looked promising, but it didn't cut it for me.
After creating a new project from any demo project, compilation goes without errors.
Immediately after this, when entering to a C file for the first time (for example, in the file with the main() function), the errors appear.