As far as I know, there´s no way to transfer a muse-site to portfolio. Portfolio is just another way to show your images or artwork. Muse is Muse and Portfolio is Portfolio.
BC is/was just another way to host sites like hosting companies but with some extra for all kind of analytics and shopping system, I guess. Never used BC, though.
Uwe is correct. Portfolio is NOT web hosting like Business Catalyst was.
Portfolio is an online site builder and hosting rolled into one package. Portfolio is easy to use and requires no coding skills. Best of all Portfolio ties in with your Behance, Lightroom & Adobe Stock collections.
Now that Muse and Business Catalyst are both End of Life, start over and create an all new website. If not with Portfolio then use something else like Squarespace, Webflow or WordPress.
Hope this helps, good luck!