can't create lightsail instances

Hello.

I think the answer to the question at this URL will be helpful.
https://repost.aws/ja/questions/QUtgCKuFFqRUW9wTaDysDztg/error-sorry-you-ve-reached-your-maximum-limit-of-lightsail-instances-0

Newer AWS accounts may be limited to a lower quota than the displayed quota.
https://docs.aws.amazon.com/general/latest/gr/lightsail.html

New AWS accounts might start with quotas that are lower than those described here.

I recommend that you open a case with AWS Support under "Account and billing" to remove these limits.
Inquiries via "Account and billing" can be made free of charge.
https://docs.aws.amazon.com/awssupport/latest/user/case-management.html