yes this is an issue. i'm missing a ton of space. Where is it!
easy enough answer for that: It's on your drive, left in unused space by what in my opinion was a mis-informed decision to erase your drive.
Whoever partitioned your drive when it was erased, decided to format the drive to 90GB, leaving you with about 140GB of unformatted space. That's your "ton of space"
This is your new MBPro, correct? (or some other 2018 Mac..)
Did YOU erase the drive on your new Mac for any reason? (Someone did ... )
If you want the space back - the simplest way to do that is to erase the drive. The BEST way to do THAT is to boot to an external drive that has a bootable system (or to a bootable Mojave installer, eh?) and erase the drive (not just the container named NewMac2018, but erase the device, which will leave you with a single partition, taking ALL the space on the drive. Then, when you reinstall Mojave, it will create the APFS container, using all the space that is available. I suspect that you (or whoever actually erased the drive decided to randomly make the drive some random drive, and you didn't need to do that. Just let the Disk Utility erase (reformat) the drive, and you will end up with what you would like, a full use of the drive.
I HOPE you had the security settings changed to allow you to boot to an external drive (you would do that BEFORE you erase the drive. If NOT, then I think your best choice NOW, is to take your Mac to Apple, let THEM figure out how to get all the space back. (I should think you are allowed, as a new user, to make mistakes, and Apple shouldn't fuss too much about setting your drive back to a proper partition scheme.

)
(That new T2 security chip can really mess things up, eh? )