iMac 2017 will not restore.

[Oldmopars]

A bit of history. My daughter bought this iMac new in 2017. She has been using it for years, but it has slowed way down recently. I reinstalled the OS, it was on Sierra. This didn't help much. I then tried to run it on Linux Mint. This was a bit better, but had issues with Sleep/Wake that drove her crazy. I switched over to Linux Elementary. It was working great on a 2011 21.5 iMac, so I figured it would work on the 2017. Sadly, no. It had the same issues and I tried several different fixes on the internet for iMacs with Linux and the 2017 just never wanted to do the sleep/wake like it should.
So, I thought I should go back to Mac OS. However, when I tried, I got an error: "An error occurred while preparing the installation. Try running this application again."
I tried several times, reformatted the drive, nothing. Same error every time.
OK, it has the old 1TB spinning disk and 8gb RAM. I have several SSHD drives, basically what Apple called a "Fusion" drive. I opened it up, installed the SSHD, put in some more RAM and put it back together. So, now it has a new drive and new memory.
I tried Internet recovery once again, and I got the same error several times.
What's next? Should I try a new version like Sequoia? I am not sure what to try next.

 

[Bigwaff]

OK, it has the old 1TB spinning disk and 8gb RAM. I have several SSHD drives, basically what Apple called a "Fusion" drive. I opened it up, installed the SSHD, put in some more RAM and put it back together. So, now it has a new drive and new memory.

Is the iMac the 21.5 4K or the 27 5K? Did the iMac originally have an internal Fusion Drive? Apple Fusion Drives are actually two drives combined using software.. an SSD and a HDD. Fusion Drives are not a single packaged drive (which I am assuming is your "SSHD"). Did you replace just the HDD component, leaving the original SSD component installed? Sorry for the questions, but your post, as I read it, is not clear regarding the original configuration and your upgraded configuration.

 

[Oldmopars]

21.5in normal IPS screen, base model. It never had the Fusion drive, just a 1TB HDD. Yes, I replaced the HDD with an SSHD.
An update though. I tried several times as I said to install Sierra, failed every time. However, I went back and tried Ventura and it is now working. "So Far" it seems to be acting very normal, the speed seems good, the internet is working good. It all seems to be back to normal. I am not going to buy the foam kit to put it back together yet as I just don't trust that it will still be good in a month. However, I will buy it and wait and see. If after a couple of months, it is still working, I will button it back up. For now I am just using some clear strapping tape.