• Define an external folder with your "proto" files and defines it in "Import Paths" menu (for instance "/home/test")
• Declare an import as:

import "EXT_LIBS/file.proto" ;

The important point is the space between the last quote and the semicolon

Then, when "Ctrl+Click" one the line the import will produce

/home/test/EXT_LIBS/file.proto\" not exists

Delete the space to write import "EXT_LIBS/file.proto";

and everything works.

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