Cannot install macOS Sierra on late 2015 IMac

Hello Everyone, I’m so lost and truly need help. I’ve read multiple forums for hours and everytime I get past a roadblock another one appears.

I recently bought a late 2015 21.5-inch iMac from somebody. When I turned on the iMac for the very first time, it made me sign into a guest account (previous user reset it and created guest account). I was able to do so successfully. However, I had issues connecting the mouse via Bluetooth to the iMac (I was able to open Bluetooth settings, find the mouse but when I’d highlight it and press enter it wouldn’t try to connect to the Magic Mouse (it runs on batteries so I could not try connecting via usb). The keyboard and the Magic Mouse both work (I was able to successfully use them on my MacBook Pro). Because I was not familiar with keyboard shortcuts to bypass having to use the actual enter key, I decided to reset the iMac via internet recovery (it’s the default recovery option when pressing command-R upon start-up) with an internet cable. Initially I tried running disk utility but it said “First Aid found corruption that needs to be repaired. To repair the startup volume, run First Aid from Recovery.” Which was weird bc I was in recovery mode. So at this point I decided to give up and just restart the iMac normally however it would go to a flashing box with a question mark error -2100f.

At this point, I realized I needed to learn how to use my keyboard as a mouse so I learned how to use voice over commands. I then tried restoring from my external drive which I use with Time Machine on my MacBook Pro but the external drive wouldn’t show up. I am assuming because this is a vintage iMac and it will not be able to operate Ventura nor recover from it. I also tried installing the macOS Monterey but it wouldn’t install in either Macintosh HD-Data-Data-Data-Data-Data nor Update.

So I then ended up erasing the internal drive labeled “APPLE SSD…” with Guid partition map and I chose Apfs as the file format. However when I then tried installing the macOS, no

Hard disk would show up for me to select. So I went and tried to create a partition under “APPLE SSD….” But the +/- button was grayed out and then I realized its because there was no container disk underneath it. (Also, I noticed it was no longer “install macOS Monterey” but “install macOS Sierra”. )

I then tried erasing the internal disk again and this time formatting it as macOS extended (journal) and I enabled journaling as prompted when trying again to install macOS on a hard drive (none showed up). At this point after enabling journaling, there was finally a hard disk to install the macOS to. BUT it failed and asked me to try again. When I run disk utility, everything checks out and it says complete.

I tried starting in safe mode, I couldn’t get it to do so. I tried running diagnostics but my keyboard keys wouldn’t register so I couldn’t click “I agree”.

I don’t know what to do, please help me install the macOS, I do want to install macOS Monterey if possible since that’s the latest software I should be able to update to. I don’t know if I did something wrong with the internal drive. (I finally got a usb mouse to not have to use voiceover etc).

what do you think the problem is? What should I try next?