@Richard S Thank you for reaching out to us, As per our documentation - https://video2.skills-academy.com/en-us/azure/trusted-signing/quickstart?tabs=registerrp-portal%2Caccount-portal%2Ccertificateprofile-portal%2Cdeleteresources-portal Trusted Signing at this time can onboard only legal business entities that have verifiable tax history of three or more years by verifying the domain via txt record wont meet this requirement.
However tagging my colleague @Meha-MSFT for more information on the above ask.