What about Publii?

WYSIWYG static site generator but personally I like to keep the content in markdown pages in a git repository so i can keep unlimited edit history; this saves everything in a local sqlite database.

Unfortunately the most powerful one that checks all the boxes, including automatic upload to s3 is hugo, but as you said the learning curve is high. Maybe try to see if you can run the example site of this theme, install hugo in your system, then go in the examplesite directory and run hugo serve. Slowly edit the files until you understand how it works.