OK, so, I still cannot reproduce the issue (yet I have a clue, see below), but I made #3427 to fix that for good and make it "functional by default".
Now, to what I think the issue is: looking at your screenshot of the *filetype_extensions.conf* file: ![f77-bug-030](https://user-images.githubusercontent.com/1883220/223740022-77398f02-cbbc-4f...) we don't really see clearly the symbols tree, but the piece we see `7 [30]` refers to the `F77` key: the line matches, and it should show up. However, it *seems* to be on the *second row of the tree*, which it should not. The tree should look like so: ![f77stree](https://user-images.githubusercontent.com/793526/224167613-8d6566e0-8bd0-4ce...) Notice that: * `F77` is on the 3rd row * `Extensions [4]` above is wider so should show up in your capture.
This leads me to believe that the issue is that you did not uncomment the `[Extensions]` section on line 4. Admittedly it's not obvious one has to do that, although [@elextr mentioned it](https://github.com/geany/geany/issues/3425#issuecomment-1458222277), but #3413 should improve the situation (and I believe, would have prevented you from most of the pain).
FWIW, this *filetype_extensions.conf* should suffice to solve the initial issue: ```ini # Filetype extension configuration file for Geany # Insert as many items as you want, separate them with a ";". # See Geany's main documentation for details. [Extensions] F77=*.f;*.for;*.ftn;*.f77;*.F;*.FOR;*.FTN;*.fpp;*.FPP;*.F77; ```