I have exactly the same experience with 2.6
I have a project based on the https server example and set up a new computer with Eclipse 2022-06 idf plugin 2.6 and imported the existing project. All was fine except the compile did not go through because uart_config_t could not be resolved and NULL was undefined.
In further investigation I found that hal/uart_types.h was not included (file missing)
so this
Normally the standard library headers are available without any extra settings.
is a dream (or a lie)
I did try what not, nothing solved this issue. Remember my project compiled and ran fine before. I have to get my project running till tomorrow. I had the idea to make a new project with the HTTPS server example and copy my view source files over.
And now it comes, when I created the simple https sample project in the same workspace THE UNRESOLVED REFERENCES DISAPPEARED in my own project. After I could CTRL-click on hal/uart_types.h and it opened. uart_config_t and NULL was defined like before.
My project compiles and runs now (almost)fine. Just because I created a sample project in the same workspace.
Please find an explanation for this. This IDE is wasting thousands of man hours around the world for this sort of issues.
For somebody who will eventually work on a fix for this issue with the IDF it might be a good starting point why I can not just copy my projects into a new workspace or just check out from my Git repo, compile and run.
I think the issue for the above explained behavior should be found in the reason why I do have to IMPORT a project from another workspace rather then just copy it on OS level.
I am very frustrated with this dev environment, working with it now more then a year. Mainly spending my time sorting out exactly these type of issues.
May god be with you
Ralph