Embedding is not available in the new viewer yet (I asked tech support, and then said only in the classic viewer) so usually I add it to the Basic template in the Instant Apps and then there is an embed option. That should be a workaround for the symbology changes.
I noticed that it does that as well - if you switch to Classic Viewer, sometimes the colors and zoom/scale gets a little weird.
For the password part - that can be changed in either viewer! That's in the share settings - you have to mark it Public in order to not have a log in. If you mark is "organization only" then it will still require a log in.
Good luck with your project!
