I've confirmed that the Marketplace UI still doesn't let us enable t4g.* and opened a support request with AWS to see if they can enable this for us.
For now, use the AMIs listed at https://wiki.debian.org/Cloud/AmazonEC2Image/Buster
- Bug#971561: cloud.debian.org: ARM-based Buster AMIs don't s... Ryan Thoryk
- Bug#971561: cloud.debian.org: ARM-based Buster AMIs do... Noah Meyerhans
- Bug#971561: cloud.debian.org: ARM-based Buster AMI... Noah Meyerhans
