https://repost.aws/questions/QUKruWYNDYTSmP17jCnIz6IQ/unable-to-set-lambda-memory-over-3008mb

an AWS support guy answered with this:

Lambda functions with memory configuration greater than 3GB are currently unavailable for first time use in some regions. We are working on restoring this feature and mitigations are in progress. If you urgently require to use your function with memory greater than 3GB, please raise a support ticket and request that the limit get raised for your account.

If your account quota shows 10GB, and you are getting this error, it could be a service glitch or capacity issue.

You can either try again later, or choose another supported region and try again.

So I believe you just need to raise a support ticket, and they'll raise your limit.