So TurboTax 2025 is using an InstallShield compiled "SetUp.exe" to install the app. Process Monitor shows that SetUp.exe does query the usual "ProductName" and "CurrentVersion" value items in the registry at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion.
However I don't think SetUp.exe is actually using the info in those value items to determine the Windows version. For instance, Windows 10 and Windows 11 both show the same CurrentVersion of "6.3". Also, my Windows 10 VM shows ProductName "Windows 10 IoT Enterprise LTSC 2021" while my Windows 11 VM shows "Windows 10 IoT Enterprise LTSC 2024". Yeah, they both say "Windows 10" there (go figure!), but show different years.
So I tried editing the ProductName registry entry in my Windows 10 VM to instead show "2024". Unfortunately InstallShield was too clever for that and it still gave me the same warning. However the TT installer does work correctly in my Windows 11 VM.
Next step will be to do an in-place upgrade of my Windows 10 VM to Windows 11. Since it's a VM, I can freely fiddle with the virtual hardware settings, including removing the virtual TPM. That way we can confirm (or deny) that TurboTax itself cares about that "hardware feature".
