parallels 16 doesn't see a mac in target disk mode as an external disk

Morning all. If I searched for and missed a discussion which is on point, then just say so and I'll rid the forum of this post. My Parallels 16.5 sees my USB devices, and additional devices are seen and usable. Except for one - I have an old Mac laptop (thunderbolt/HDMI) booted in target disk mode which I would like to use as an external drive. My new laptop is all USB3/TB3. I'm using Apple's own USB3 to original Thunderbolt adapter to Apple's own TB cable. This mounts the old Mac natively on my new Mac, but Parallels doesn't even see it. The problem is most likely at the hardware level because choice of VM (macOS 10.14 / Ubuntu / Win10) doesn't make a difference. Does Parallels normally not detect Macs in TDM? thanks, h