High Sierra MacBook Pro 2012

I am confused.

The second paragraph here states: "Fusion drives, traditional hard disk drives (HDDs), and non-Mac drives aren't converted [to APFS]."

Prepare for APFS in macOS High Sierra - Apple Support

... I was informed that the latest version of High Sierra is using a new file format, which is designed for SSD drives and that will result in all kind of trouble on older Macs (like my MBP 2012) that use HD or SSHD.

That is not true. Although APFS (a file storage system) is designed to be used with flash memory, that fact does not matter to High Sierra (an operating system). The operating system does not care about the underlying file storage system and runs just fine on traditional rotating hard disk media.

As a result, I lost about 3 months worth of data+work... (due to the new file format used, since you cannot use TimeMachine to backup your data in High Sierra and then recuperate it in Sierra).

That is also not true. There are no justifiable reasons to ever lose data. Time Machine works exactly the same way it always has, and you can can restore a backed up system the same way you always have. That's the reason creating a backup is Step 1 of Apple's macOS upgrade instructions.

Why doesn't Apple inform their MacBook Pro 2012 users that upgrading to High Sierra will result in possible freeze of the system?

That's the only question I can find in your post, and the answer is "because it does not". I have personally upgraded 2012 model MPBs as well as models older than that. No problems.

If you are having trouble with your Mac, ask here first. The "lags and issues" you describe were not caused by its operating system. Complaints such as yours have arisen with every Mac operating system upgrade there has ever been, and will continue with every operating system upgrade there will ever be. The years have passed but the usual causes remain the same. It's not the OS.

claudefromblainville wrote:

But Dear Apple, this is difficult to forgive... if you are aware of some compatibility issues when you release a new OS, make sure that you inform your clients before you push them to upgrade...

Claude

FWIW, Apple is not here. This is a users forum. When upgrading to High Sierra it will only format to APFS on SSDs.

It's hard to know what may have happened or why the "Genius" would have installed Sierra. The "lags and issues" could have been caused by any number of reasons.

After installing High Sierra in multiple Macs I'm comfortable saying whatever the problem was, it wasn't because of High Sierra.