kvormwald,
Instead of "Get Info" and "Hide Extension", you may try this:
• click filename once, then a second time, like to rename it (not double-click)
(only main part will be selected, not the file extension)
• enter Cmd-C to copy the filename (the part before "." and file extension)
• enter Cmd-A to select all of the filename (name and extension)
• enter Cmd-V to paste over the whole filename and extension
• click on an empty space or enter Return
– once used to do it, you can do it pretty fast
This will get rid of the visible file extension, but it will remain as invisible. No need to open the "Get info" window. For me, it is quicker that way.
It does work for any file type, like image files (png, jpg, heic, etc), Microsoft documents (excel, word, power point, etc), Safari shortcuts (.webloc), pdf, txt, and more. You may not have noticed, but they all do the same buggy behaviour with their file extension.
Note:
Another way, if you prefer to see the Info window, is to select the file by clicking once on it, then:
• enter Cmd-I (short cut for get info)
• click the Hide extension check box
• enter Cmd-W (short cut to close the get info window)