For upgrade from win10 to win11 “without” the TPM (even though it’s there), create a USB installer using the media creation tool, then open an admin command prompt, change to the stick’s drive and issue setup.exe /product server.

That inhibits all the checks and (aside from branding it as server during the install process) will allow you to perform a win10 to win11 upgrade on completely unsupported hardware, but in this case the Pluton TPM will be detected by win11 once booted.

I’ve used this on a couple of my old machines now just for giggles and it works really well.