Linked Staff not working (for me)

In the dialog box of instruments (shorcut "I"), it's always greyed out, as you say, because you don't select at the right place.
Probably you click on the instrument name, like this:

1)You must click on "staff1", and consequency, you may add a staff or a linked staff. See:

2)Then, for change (or not, depending your choice) the staff type, you have to choose the staff type by opening the drop down list at the column right: for this, click on standard (default) second staff, then eg click on Tab. 6-str. simple (then: Next -> Next -> Finish)
And so, the two staves are linked now, as you wish.

Finally, by the same way, you may add another staff when you want, linked or not, at the same initial step #1, or later, after the step #2, by returning in the dialog box ("I")

What goes wrong when you try?

This is what you should be doing:

1) Select one of the guitar instruments from the list at left. Either tab or standard; whichever one you want to appear on top

2) Press "Add"

3) Click where it says "Staff 1" at right

4) Click "Add linked staff". This will add another staff of the same type (standard or tab)

5) Under "Staff type", use the drop down menu to change it to the other type

6) Press "OK".

Your assessment is true, and the Handbook *does* state this:

"Once the new linked staff is created, you will usually want to change its type (e.g. to tablature) and/or change its type properties, as described above."

But it's pretty buried in a long complex page.

It's always much easdier to offer help if you post the actual score you are having trouble with., From a picture, we can only guess.

But here are some guesses:

1) you can only add a tab staff to an instrument that is actually defined to be able to use tablature, like guitar or ukulele. Piano cannot use tablature because it would not make sense.

2) The "Add linked staff" button, like the "Add staff" button, adds a staff to the currently selected instrument. It does not add a new instrument; that's what "Add instrument" is for. So if you have the piano staff selected, then "Add linked staff" will always add another piano staff, not a new instrument. The list of instruments at left is for adding new instruments to your score, not adding staves to existing instruments.

3) To change the instrument used by a staff, right click the taff, Staff Properties, then press the Change Instrument button

4) Yes, with the linked staff feature, you can add the notes first then add the linked staff. It works very well.

Great! For the record, it is normal for music of only a single instrument to not print an instrument name. The name of the instrument would normally be in the top left for parts generated from a larger score, or on the front cover for a collection in a book, etc. But fi you ever do want the staff name printed for music of a single instrument, just go to Style / General and uncheck "Hide instrument name of there is only 1 instrument".