Link piano stave to ukulele tab stave

Of course not, you can only link staves for the same instrument.

I converted your score so it now has linked ukulele tablature. (Didn't see that cadiz1 already had!)

      Let There Be Peace On Earth with linked Ukulele TAB.mscz

The steps were as follows:

a) Delete the unlinked ukulele staff

    1) in normal score view press i (for instruments)
    2) select the ukulele track
    3) press the trash can icon to delete it
    4 OK the dialog

b) change the Instrument type

   1) in the Instruments Panel, click on the gear to the right of "Piano"
   2) press the Replace Instrument button
   3) under the Instruments column, type "uku" in the search field
   4) due to the range of your melody choose "Ukulele (Low G)"
   5) OK the dialog
Alternately you can use the following for step 1
  1) in the Instruments Panel right-click your piano staff and choose Staff/Part Properties

c) Add the linked staff

... back in the score
   1) in the Instruments Panel, under Ukulele, click on the gear to the right of the Treble Clef staff
   2) click "Create a linked staff"
   3) click on the gear to the right of the [LINK] Tablature 4 lines staff to choose the desired TAB staff style

You don't have to do all this every time. Just save the attached score somewhere as a "template."

I thought you could simply open a ukulele template (File>New Score>Create from Template) and enter your notes into it. But surprisingly I see no ukulele template, even on searching for it.

Saving your own custom templates

You can save custom templates in MuseScore 4.
NOTE: Whenever I search in the "Search for "custom templates" via the Search for Help field the results are specific to MuseScore 3

You can see the default MuseScore 4 custom template folder listed under:

    MuseScore > Preferences > General > Folders > Templates

Here on my Mac the path is

     /Users/John/Documents/MuseScore4/Templates
(I don't know what the equivalent is on other operating systems)

Note Your custom templates are not necessarily shown under the File>New>Create from Template.
To see them:
    1) choose File>New
    2) click Create From template
    3) Then click My Templates under Category column
    Oddly, the Template search field doesn't search the custom template folder.

scorster