Can’t you just use Migration Assistant or TimeMachine restore?
Regarding the .cleverfiles folder!:
Do you use or did you ever use Disk Drill, a disk utility published by CleverFiles. Disk Drill creates the folder .cleverfiles to help recover files or folder.
You can boot your Mac Mini in target disk mode. That way you can use it as an external thunderbolt drive.
You can get a thunderbolt 2 to thunderbolt 3/usb-c adapter (Apple sells one). But you can get yourself a 1TB external SSD for about the same price as the adpater!
Try this:
Use terminal in recovery mode to change the date to 2011,
date {month}{day}{hour}{minute}{year}
example:
date 010101012011
Maybe it works, maybe not, but it doesn’t hurt to try!
Sorry to correct, but:
Cmd-R lets you re-install the previously/currently installed MacOS on your Mac (not applicable in your case, since no bootable/recovery partition is available).
Cmd-Opt-R lets you re-install the most latest compatible version of MacOS on your MacBook.
Shift-Cmd-Opt-R...
The question mark only indicates that your MacBook does not have avalid boot/startup partition.
On Intel-based Macs, power on your Mac (or restart if already on), and press and hold the Cmd + Option + R keys immediately on hearing the startup chime.
This will boot your MacBook in Recoverymode...
I would suggest to stop try using MacOS screen sharing options. Do you only need access to the old iMac to provide remote assistance?
Try installing TeamViewer QS on the old iMac and install TeamViewer (free for non-commercial use) on your mac.
This way you can provide remote assistance without...