Question about Canon Pixma Ix6850

I use the printer on my MacBook Pro with BgSur and have had no problems so far.
However, I do not use the OSX standard / suggested printer driver, but the one from Canon.
Yes and it is always necessary to make some settings in the printer dialogue with the variety of printable media.

I don't know because I work with WIN10.
I have never had smudged photo paper pages. I use compatible photo paper and cheap compatible print cartridges. This works great. If exact representation of colours is desired, one can have the printer calibrated, i.e. an ICC profile is created, which is integrated into the printing software and good. I have done this and the prints differ only slightly from professional lab prints.

Yes, it is. Important: if you don't tell the printer exactly what kind of paper it has in the tray, it will print incorrectly. To do this, you have to dig through the menu functions. Glossy paper should only be printed on individual pages at a time. If it pushes the printed pages on top of each other, it smears the ink that has not yet dried. If the printer is not used for a few weeks, everything dries up and nothing works. Check the ink prices before you buy!