lightsail access

As per https://aws.amazon.com/free (screenshot below), Lightsail is currently exclusive to paid plan, and is not available if you are on AWS free tier

Once you are on paid plan, you can use Ligthsail on free trial as per https://aws.amazon.com/free/compute/lightsail/?

Yes, you can access Amazon Lightsail on the free trial. Lightsail offers a 90-day free trial for new or existing AWS accounts that started using Lightsail on or after July 8, 2021. This free trial is separate from the general AWS Free Tier.

During the 90-day free trial period, you get 750 hours of usage per month on eligible plans, which is enough to run one instance continuously for an entire month. The free trial applies to select Lightsail bundles, including certain Linux/Unix and Windows plans.

Interestingly, the Lightsail free trial is separate for Windows and Linux instances, allowing you to take advantage of both simultaneously. You can run up to 750 hours per month of a Windows instance and 750 hours per month of a Linux instance during the trial period.

If you're having trouble accessing Lightsail, it could be because:

1. Your AWS account is newly created and not fully activated yet (may take up to 24 hours)
2. You haven't completed the sign-up process for your AWS account
3. Your payment method isn't valid (even for the free trial, a valid payment method is required)

If you encounter an "It looks like you aren't authorized" error, try waiting a few minutes and refreshing your browser. If the problem persists, you might need to contact AWS Support.
Sources
Does Lightsail Fall Under the AWS Free Tier? How Can I Track My Usage? | AWS re:Post
Lightsail 3 Months Trial - Windows and Linux seperate? | AWS re:Post
AWS Lightsail Access | AWS re:Post