Manual Focus works great with a Z6, perfect body for adapting MF-optics.
You can set a lens number and enter the focal length + the maximum aperture for each lens, with the Non-CPU lens data option of your Z6.
As long as one remembers to preselect the appropriate non-CPU setting, you get 3-axis IBIS with the Z6 with each of your Non-CPU lenses.
Furthermore, you have the option of focus peaking + the magnification option, which gives you precise focusing feedback.
I use a lot of old MF-glass, see my gear-list, Canon nFD, Mamiya 645 Sekor, M42 and it works very well with all my MF-optics, some of which, like my Canon nFD 85mm f/1.2 L, have really gained adapted.
Amazing how well some of my 40-50 year old optics perform with a body like the Z6.
With the native Voigtländer 35mm f/2 Apo-Lanthar Z it's even better, with electronic contacts and full communications between the lens and the body, Exif information, + focusing by color changing of the focus point frame, but it's fine the way it is with the Non-CPU lenses.