I obtained a licence key for W10 Pro and activated successfully, but it hasn't helped. Not that the licence is wasted, since I will eventually need it anyway.
But, some progress in understanding, at least.
It appears that only Insiders who have been getting updates before 24th June were allowed to get W11 updates without TPM. Since I came onboard just after that, I don't qualify.
But now I am stuck some kind of loop. I am in the Dev channel, but the insider program was supposed to move me back to the W10 Preview channel (since my hardware doesn't qualify), and I need to be there to continue to get updates on W10 (e.g. 21H2 build 21390) - but the program didn't make that move. And my settings doesn't give me any way to move out of the Dev channel manually, so I am continuing to be offered un-installable W11 builds and no W10 builds. I suspect that I will have to withdraw entirely from the Insider program and start again, but I am concerned that might crash my whole Parallels Windows VM. And I can't find out whether Microsoft will let me back in again if I once opt out.
Any ideas on how I can break this loop?