accidental monterey installation on other partition (lost data)

[YENNI]

Hi, I am here to seek a big help.
I am not an expert in mac, just a regular user.
I have a macbook air 2018 and used it since January 2019.
I have two partitions in my mac, Machintosh HD and one is using my name (Yenni)
Today I made a big stupid mistake causing all my data gone
I tried to upgrade my macOS from mojave to Monterey, but when I tried to install the Monterey, it gives only one disk option: Yenni, because the other one is not active due to not enough storage (it said it need to free up 8 GB for installation)
so I chose the other disk and follow all the instruction, Then it asked which mac to transfer then I chose Machintosh HD, then it started making me anxious when it looked like I am installing a new MacBook, it asked my region, language and so on.
After finishing then I see that all the data in my Yenni disk have disappeared, changed with a new look
Can anyone advise me whether all the data can be recovered?
Or should I just accept this reality: all my data has lost?

 

[YENNI]

Hi, I am updating this post
After trying to restart from the old disk (machointosh HD), I opened the other disk (name Yenni-data), and besides folder for applications, library and users, there is one folder name previous content. And when I opened this folder all my data exist there. thank God!
now the problem I have two systems in my mac, mojave and Monterey. great thanks if anyone can recommend what best step to do now

 

[Fishrrman]

Which OS do you want?
Mojave or Monterey?
(my preference is for Mojave.)

We need to know this before going further.

 

[YENNI]

Hi,I prefer monterey because I need to install software that cannot be installed with Mojave.
thanks in advance

 

[richmlow]

Hi, I am updating this post
After trying to restart from the old disk (machointosh HD), I opened the other disk (name Yenni-data), and besides folder for applications, library and users, there is one folder name previous content. And when I opened this folder all my data exist there. thank God!
now the problem I have two systems in my mac, mojave and Monterey. great thanks if anyone can recommend what best step to do now

Hello Yenni,


I'm glad that you still have your critical data!

Before you do anything else, the first thing that you need to do is make another BACKUP of the critical
data which is separate from your two disk/SSD drives. That way, you will have more peace of mind.


richmlow

 

[Fishrrman]

First, you need to get your personal data backed up onto an external drive, so it's safe.

Do you have an external drive of some sort?
USB3 would be the best.

What I would do:
- create TWO partitions on the external drive, both APFS.
- on one partition, I'd use CarbonCopyCloner to clone your Macintosh HD volume (the one with Mojave on it). This has your applications and accounts.
- on the other partition, copy the folder named "previous content". This has your personal data files.

CarbonCopyCloner is FREE to download and use for 30 days -- won't cost you anything to use it.
You've got to get this stuff to a "protected place".
DON'T GO FURTHER until you're "backed up"

Then...
I'd boot to INTERNET RECOVERY:
Command-OPTION-R
at boot

You'll need your wifi password and the internet utilities will take a while to load.

When you get to the internet utilities, open disk utility.
Go to the VIEW menu and choose SHOW ALL DEVICES. IMPORTANT that you do this!!
Now, look at "the list on the left".
The top item should be the physical drive itself.
We're going to ERASE it. (this is why you have to be backed up!)

Click the erase button and choose APFS, GUID partition format.
DO NOT PARTITION THIS DRIVE.
When the erase is done, quit disk utility.

Open the OS installer.
It should offer you Monterey.
Start clicking through.
The MacBook will restart one or more times, and the screen will go dark for a minute or two with no indication that anything is happening, so be patient.

When the OS install is done, begin the setup.
Have your backup drive ready.
At the appropriate moment, setup assistant will ask if you wish to migrate from another drive, etc.
YES, you want to do this. So....

Connect the backup drive and point setup assistant to it.
You want to choose the drive named "Macintosh HD", which has your apps and accounts.
Setup assistant will take a while to "digest" things, be patient.

When done, you will see a list of stuff that can be migrated.
I suggest you migrate ALL of it.
Setup assistant takes a little while, be patient.

When done, you should see your [older] login screen, so log in and "look around".

Does it look ok?

If so...
Now you will probably need to move stuff from the "yenni" backup to the new OS volume.

Instead of a "partition", I suggest you just create a folder named "yenni", and store personal data in a folder/file hierarchy within it.
This way, you can back up the Macintosh HD drive and the yenni folder (and contents) will be backed up as well.

And I ALWAYS recommend using either CarbonCopyCloner or SuperDuper instead of time machine.

Print this out for reference.
Good luck.