HELP: At wits end trying to migrate MacOS 10.13 High Sierra to UTM on macOS 26 on M4

[the-Algol]

Following the helpful instructions (with links to the UTM configuration and MacOS ISO files) at How to run macOs 10.14 High Sierra on Mac M1 arm silicon, I have a VM with macOS 10.13 High Sierra running on my new MBB with M4 running macOS 26.

Every attempt at migrating my existing 10.13 system on a late-2011 MBP to the VM fails. Both machines are on the same Ethernet and Wi-Fi network. My user credentials are the same on both. I've been beating my head against this for days, I bought the M4 laptop specifically to move my 10.13 and my 10.6.8 systems to it, along with my everyday Intel 2019 MBP. Apple lets you return a new machine within 14 days, which will be up in a few days. At this point, I'm so frustrated that if I can't make progress, I'll just return the machine and maybe try again late in the year in the hope that UTM will work better on Macs by then. Please, if you know how to move past this, let me know.

• I put the 10.13 MBB into target disk mode, plugged a Firewire cable into it, connected the other end into the macOS 26 M4 MBP using a Firewire to Thunderbolt adapter, but the M4 MBP doesn't see the 10.13 drive.
• I connected an external Firewire drive to the 10.13 MBP and did a Time Machine backup to it. I connected the drive to the macOS 26 M4 MBP using a Firewire to Thunderbolt adapter, but the M4 MBP doesn't see the drive.
• I plugged a USB drive into the 10.13 MBP and told Time Machine to do a backup to it. I shut down the VM, edited it to add a removable USB drive, and started it up, inserted the USB drive into the M4 MBP, UTM asked if I want the VM to access it, I said yes, the macOS 26 on the M4 MBP asked if I want UTM to have access, I said yes, and immediately macOS 26 put up a scold dialog telling me to eject the disk before removing it. The guest Mac doesn't see the USB drive, and neither does the host MBP.
• I edited the VM to use bridge mode networking, started the VM, ran Migration Assistant on the 10.13 MBP. The guest MacOS sees the 10.13, I select it as the migration source, and then it says it is unable to access the 10.13 MBP.
• I tried with Shared Networki, but then the guest MacOS doesn't see 10.13 machine at all.
• I tried with Virtual Network, but again the guest MacOS doesn't see 10.13 machine at all.
• I put the 10.13 machine into target disk mode, plugged it into a third machine using a Firewire cable. Using Disk Utility on the macOS 26 M4 machine, I created a blank disk image on the macOS 26 M4 machine, mounted this disk image using Disk Utility on the third machine, and attempted to restore from the 10.13 machine's boot volume into the disk image. Disk Utility runs for a while, then exits with a timeout. This happens repeatedly.
• I put the 10.13 machine into target disk mode, plugged it into a third machine using a Firewire cable. Using Disk Utility on the third machine, I created a disk image from folder. Disk Utility starts and then immediately gives a permissions error. This happens repeatedly.
• I created a blank disk image on the macOS 26 MBP, mounted it on the 10.13 MBP, and told Time Machine to back up to it. It told me I don't have the right permissions. I tried mounting the disk image using my own login credentials as a registered user of the macOS 26 machine, and using an Apple ID. Same results either way.