Regarding the Babel issue. I had a reply back from support, and the following worked for me:
Try changing the browser list file in the root of the project to the following;
# This file is used by the build system to adjust CSS and JS output to support the specified browsers below.
# For additional information regarding the format and rule options, please see:
# https://github.com/browserslist/browserslist#queries
# You can see what browsers were selected by your queries by running:
# npx browserslist
last 2 Chrome versions
last 2 Safari versions
last 2 Firefox versions
This now builds locally and and on AppFlow