Mac mini increasing HD size

A hardware drive dock copy as you describe would be equivalent to using the command line dd tool and would therefore result in the problem you had.

I do regularly use drive docks but I use ones that merely connect the drive to a computer and then I use (mainly) CarbonCopyCloner to do the actual copying. I would not use the dock itself to do the copying as explained by HWTech.

For the scenario of wanting to copy from an old drive to the new internal drive I would normally do the following.

1. Boot from the old drive
2. The old drive could initially be still internal or as you have already swapped it could be in a drive dock which is connected to the Mac mini
3. Make sure the new drive is formatted as partition type GUID and volume format APFS
4. Run CarbonCopyCloner and specify the old drive as the source drive and the new drive as the destination drive, I would disable snapshots, and tell CarbonCopyCloner to copy all files and to turn the safety net off
5. When finished shutdown
6. Disconnect the dock and hence the old drive
7. Reboot - it should boot from the copy i.e. on the new drive

What method did you use to do the cloning?

If you used the command line dd tool it might result in this. If you used CarbonCopyCloner or similar these are file copy tools and should not result in this. If you used the Disk Utility 'restore disk' option this is a block copy tool but has (in theory) the intelligence to resize volumes on restore.

I would normally recommend downloading a trial copy of CarbonCopyCloner and using that.

It should be noted that APFS makes life more complex. I have found Disk Utilities 'restore' function to be particularly unhappy with APFS volumes whereas CarbonCopyCloner worked fine.

Yes, those cloning docks make a clone to the exact same size as the original. You can try using Disk Utility to resize the volume, but make sure you have good verified working backups first as there is always a possibility of something going wrong. Just make sure you have permission to resize the drive as some organizations don't like end users making system level changes to the supported computers.

The IT guys should really use Carbon Copy Cloner (CCC) as suggested by John when cloning a Mac drive unless it is being cloned to an exact matching size drive (even then I would use CCC). A CCC clone only copies the used area of the drives so it copies more quickly and produces less wear on the drives.

You should be able to use Disk Utility (in Applications > Utilities) to expand the partition to use the full 1TB. For full details see this 2019 article https://www.lifewire.com/resize-mac-disk-utility-volume-os-x-el-capital-later-3573395

Do backup first using your preferred option (eg Time Machine) to be sure, to be sure :)