The project was moved from Eclipse 2020-12 to Eclipse 2023-09 and the indexer works fine in the 2020 version. It compiles in both versions.
All the other standard containers (vector, list, etc) are properly recognized by the indexer with the only exception of the "map" template. The include works and std::map is properly referenced to "stl_map.h" when asked but any declaration of a map has always "Invalid template arguments" and map members are not recognized.
At first glance the configuration is the same between both projects and the Preprocessor Include Paths are checked and equal. The problem persists in newly created projects.
The dialect in both cases is: c++2a
Does the Eclipse 2023 indexer need a newer MinGW version?
Updating to the latest Eclipse version solved the problem.
Updating MinGW didn't fix it.
(Information provided just in case someone experiences the same issue on similar versions)