Elastic Beanstalk: unclear errors in environment creation

I'm creating an Eleastic Beanstalk environment from the console. In the "Configure instance traffic and scaling" I've entered some typical settings: root volume on gp3, 1 existing security group, load balanced, 1 instance type, internal network load balancer. When I click on "Next" I get the following, rather obscure error message:

There were 2 validation errors: * InvalidParameterType: Expected params.OptionSettings[16].Value to be a string * InvalidParameterType: Expected params.OptionSettings[17].Value to be a string

I'm reviewed the input several times but I can't find the error or what these setting 16-17 might refer to.

The only other strange thing on this page is that, regardless of which architecture is selected (x86_64 or arm), only the x86_64 instance types are offered, for example t4g optionas are never offered.