Ways to Keep Aperture 3.6?

That should work. To reboot into another OS version, go to System Preferences/Startup Disk, and select the OS you want to boot into. Or you can hold down the option/alt key when rebooting and choose the OS you want. There are no real risks or down sides as long as you have the disk space/drives to give you adequate space.

It is easy to boot between discs. Aperture will work with macOS Sierra and High Sierra. Aperture as you know is no longer supported by Apple therefore from about early Jan 2013 the RAW camera support ceased being updated so any newer cameras from that time on will not be processed when you import them, it will just be notified as an unsupported file format. Using Adobes DNG converter (it's free) you can convert newer cameras RAW images to their .dng format which you can then import to Aperture and then edit as you would normally.

Adobe Digital Negative Converter

My MacPro is running El Capitan, Sierra and High Sierra all with Aperture 3.6.

If you decide to upgrade to one of the newer OS's and decide you would like to use Aperture with it you may find that the Aperture app icon in the Applications folder will be greyed and crossed out meaning you cannot launch it. Please read this thoroughly to get Aperture working with the newer OS's.

Updating to Aperture 3.6 After the Release of Photos

Yes the EOS 1DX II is supported as you pointed out, but not the Canon 5D Mark IV as it came after the cutoff for Aperture and iPhoto, any new camera raw support is included in the latest High Sierra updates (no longer the standalone updates we used to get) and only Finder, Preview and Photos will be able to process them.

Digital camera RAW formats supported by OS X El Capitan - Apple Support

Digital camera RAW formats supported by iOS 10 and macOS Sierra - Apple Support

Digital camera RAW formats supported by iOS 11 and macOS High Sierra - Apple Support

Still like Aperture and use it, any newer cameras that are not supported I convert using DNG converter.

Oh yeah I wrote 2013, well that is completely wrong, Aperture was still supported then, it wasn't until Yosemite 10.10.3

came out in March/ April 2015 and the Photos app was introduced that Apple stopped supporting iPhoto and Aperture, and I think (crossed fingers) that the last Camera Raw support for those was in 2016.

What camera do you have? If you let me know I will download some raw files and import them into Aperture.

Thanks for pointing that out.

Canon EOS 1DX Mark II. But there’s no need to download, I’ve imported into aperture and worked with raws from that camera several times, and can confirm that they are supported. Maybe aperture can support the files as long as macos does?

I’m going to refute myself, I just tried to import a cr2 from a 5D Mark IV and it’s not supported. Now, the 5D Mark IV was released in september 2016.

The only reason I can think of is that somehow aperture can deal with raw formats supported with mac os up to “El Capitan”, but not with those whose support was added with Sierra and later.

So I guess I just got lucky, because even as I moved to Capture One Pro, I still love aperture and really wish they brought it back.

I think the part in which you state that raw files from cameras released after 2013 is not completely accurate. I have a camera released in april of 2016 and the raws import and work just fine.