glimmer.js IE Support

a new untouched glimmerjs app with ember new my-app -b @glimmer/blueprint ran in firefox and chrome but not in ie or edge.

Edge gave me following error:

SCRIPT1028: Expected identifier, string or number: 
app.js (3386,11)

IE11:

SCRIPT1002: Syntaxfehler
app.js (7,1)

After adding IE11 in config/targets.js the app runs with "Microsoft Edge", but still not with IE11.

IE11 provides following error, which referes to a let Symbol:

SCRIPT5009: "Symbol" ist undefiniert
app.js (9804,1)

Any other settings we need to change?

Also it's a little bit strange that with setting IE11 the Edge problem got fixed.

Or that the default setting 'last 2 Edge versions' does not transpile to a edge compatible version...