Hacked together this very ugly standalone Amazon SES library for the Python 2.7 / App Engine relics out there - it was such a chore and required so much trial and error that I almost was going to re-write the entire project on NodeJS / App Engine instead
Amazon deprecates AWS3 signing for AWS4 this month, so this will allow you to just keep on using SES without diving deep into the rabbit hole
And the obligatory remark about why GCP is making us suffer like this and promote other cloud services and so on