Hey Tim-Fisher! So the reinstalled finished without error? But still booted to the “?” Folder?
Typically if I do see that, I’d boot to recovery mode like you did, hit the Apple icon > Choose Startup Disk > Macintosh HD > Restart.
On another note, I believe that resetting the pram (nvram) still resets the startup disk preferences to default, but since you’ve already erased, I wouldn’t bother unless another drive is connected.
So since you’ve already removed the partitions.......Can you try erasing the main disk? (Click Macintosh HD, on the top menu View > Show All Devices), then above the twin Macintoshs’ (As I call them), you’ll have a Container Disk and above that, the main SSD/HHD/Fusion Drive, etc?
Id hit that > Erase, and make sure to choose APFS as the format and of course GUID as the partition map? Then erase then reinstall again.
Unless, after erasing its attempting to install Mac OS Sierra or earlier, then I’d choose the format of Mac OS Extended Journaled, then erase/reinstall.
Speaking of erasing then reinstalling, have you tried erasing/reinstalling from internet recovery instead? (Depending on the OS, will install a different version via the Internet)?
https://support.apple.com/en-us/HT201372
Could be an issue with the hardware otherwise, hope it’s not, but you can also try erasing/reinstalling from a bootable installer:
https://support.apple.com/en-us/HT201372
In case there’s an issue with the local recovery partition, that may be the key, otherwise I might try running hardware diagnostics to see if something else is going on:
https://support.apple.com/en-us/HT202731
Hope all works out and this helps!