EmBitz

If I right click on a function and select "find implementation" in main.c, it only finds the function it it's in main.c.
It it's in a library, for example HAL_Delay(), I get a Warning: Not found: HAL_Delay.
However, "find functions called by" is working.

"Find implementation" uses the Code Completion plugin which is not really state of the art.
"Find functions called by" uses the external Cscope tool by the Cscope plugin (as Calling and References)

It would be really nice when this can be fixed.

I agree, but it isn't a matter of fixing but building.