Hi,
The list should contain more items. Could you please try to create a new cluster using UI, set the compatibility level to 4.6, architecture to x86_64 and check the CPU Type dropdown again? Please try to scroll down the dropdown and if there are no more values than you've already mentioned, please try a different browser to rule out the possibility it is some kind of UI issue.
If the UI looks fine, you may try to check the configuration values in the database by running this DB query:
select option_value from vdc_options where option_name = 'ServerCPUList' and version = '4.6';
The returned configuration should contain the AMD CPUs.
Please, share your findings.
Regards,
Lucia