The Panasonic Leica 8-18mm f/2.8-4 is a very versatile lens and according to PGN very sharp on the Panasonic GH5. I would like to give the combo a try someday when things slow down on the other sites or the prices drop. I included the blogging with the Panasonic Lumix TZ90 video below because it includes some Panaleica 8-18mm f/2.8-4 footage.
Panasonic Leica 8-18 mm: B&H Photo / Amazon / Adorama
Panasonic GH5: B&H Photo / Amazon / Adorama
Panasonic Lumix DMC-ZS70: B&H Photo / Amazon