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Reset it to defaults (Menus under tools). Put it in P mode forget any manual M mode. Set the ISO to 200. Put the lens in AF and go outside on a sunny day. Take some shots. If it doesn't work, return it. It is defective.
What lens(es) are you using on the camera?
I ask because there are a lot of third party, manual-focus-only lenses available in the M-mount that don't connect electronically with the camera (and you mention manual focus). When one of those is on the camera, it doesn't "think" any lens is installed and won't be able to take a shot until you make a setting in the menu.
If using one of those types of lenses, look in the menu for a setting that enables the camera to "shoot wihout lens" (....even though there's actually a lens on the camera... Quite a few people have had easily solved "problems" with the camera, when they first tried to use third party, fully manual lenses and didn't know this setting was necessary.)
I don't have an M6II, but another possibility... some cameras have a "focus trap" method that can be set in the menu. This prevents the camera from taking a shot until focus is achieved. I don't know if the M6II has something like this or not. But it's something you might check.
Further, with these manual focus/manual aperture third party lenses... if those are what you are using... can only be used in certain exposure modes. M (manual, no Auto ISO) and Av (aperture priority auto exposure) should work. I don't know for certain, but it also might be okay with this type of lens to use "M with Auto ISO" (which is no longer "manual"... it's another form of auto exxposure). With these lenses, you cannot use P, Tv or any of the "Scene" exposure modes.
If using a Canon EF-M lens or another lens with electronic connectivity, temporarily remove the lens and check that the electronic contacts on the rear of the lens are clean and clear of any obstructions. If cleaning of those contacts is needed, use a clean, lint free cloth slightly dampened with isopropyl (rubbing alcohol) to wipe them.
Also look at the corresponding pins just inside the lens mount. Those are spring loaded to make good connection with the lens contacts. See if any of them are "stuck" and not extending properly. If you see one (or more) that have gotten stuck to prevent them from connecting with the camera, you might be able to carefully free it up with a toothpick or fingernail. Just be very careful not to touch the camera's image sensor, since it's right next to those electronic contacts and is exposed while the lens is off the camera.
Finally, it may be a problem with the battery or the battery charger... Are you certain the battery is getting fully charged? There should be a battery level indicator on the camrea, which will tell you if the charge is low (other Canon I use also flash a warning when it gets low... I imagine M6II does the same). Low battery might allow some things to function, but not others.
These are just some possibilities. It's also possible that there's some fault with the camera or the lens. If you have tried multiple lenses and the same thing happens with all... it's more likely the camera. Seeing how you just bought it, if none of the above helps I'd recommend contacting the seller about making an exchange. If for some reason that's not possible, contact Canon under the warranty program.
Hope this helps. The M6 Mark II seems like a really nice camera, just reading about it.