Following the instruction for alb module of Terraform https://registry.terraform.io/modules/terraform-aws-modules/alb/aws/latest
I can't understand how to disable HTTP/2 can you help me?
Judging by the module requirements, the enable_http2 variable is optional [1] and by default set to true. You can change that by adding this variable when calling the module and setting it to false:
enable_http2 = false
[1] https://github.com/terraform-aws-modules/terraform-aws-alb/blob/master/variables.tf#L19-L23