Adding DB to my RDS I do not see t2.micro or t3.micro options

It appears that the availability of t2.micro and t3.micro instance types for RDS has changed recently, which is why you're not seeing these options when trying to create a new database instance.

For PostgreSQL specifically, t2.micro instances are being phased out. AWS has been sending emails to customers with existing t2.micro instances, informing them that these instance types will reach end-of-life on March 11, 2024.

As for t3.micro, while it's still supported for some RDS engines, its availability may vary by region and specific database engine version. The fact that you're not seeing it as an option suggests it may no longer be available for new instances in your region or for the specific PostgreSQL version you're trying to use.

To create a new database with similar capabilities and pricing to your existing db.t3.micro instance, you have a few options:

1. Double-check that you're selecting the exact same PostgreSQL version as your existing instance. Sometimes, newer versions may have different instance type availability.

2. Consider using the next available instance size, which might be db.t3.small or db.t4g.micro (if available). While these may be slightly more expensive, they're likely the closest alternatives to your current setup.

3. If you need to maintain the same cost, you might want to explore using Amazon Aurora Serverless v2, which allows for more fine-grained scaling and potentially lower costs for small workloads.

4. Contact AWS support to inquire about the availability of t3.micro instances in your region for your specific use case.

Remember that AWS continuously updates its offerings, and instance type availability can change. It's always a good idea to check the most recent AWS documentation or consult with AWS support for the most up-to-date information on instance types and pricing for your specific region and database engine.
Sources
RDS InvalidParameterCombination - Combination working before | AWS re:Post
EB webconsole bug - not possible to create new environment - Error describing database options | AWS re:Post