I have the same issue as everyone else here, except none of the workarounds work for me. I lose all coloring and bolding and bullet points. Worse for me though is that it is stripping links. I'm copying a report from a report generator that I need to send out to multiple people, and it has links to files and webpages in it, but those links are gone.
After pasting, I don't get any little popup at the bottom of my pasted test allowing me to choose new formatting. And the paintbrush in the Format Text ribbon doesn't do anything different.
I have to send out this report daily, so this is a huge problem for me. I don't know that I can use the new Outlook until this is fixed.
(Today I've pasted it into a Word doc, because Word keeps the formatting and links)