Using this plugin on 'portfolio' pages

Hey,

Plugin shows up fine on posts, not on pages however on the new WordPress.
However the advanced settings override the pages easily.

However, currently I have it set to show posts on another theme, works great, pages works too, but I use a page as the homepage so want to avoid using that setting (i can only used advanced here, so setting all pages rather than individual, but fine for my need)

The theme I currently use, adds the ‘portfolio’ section to the wordpress menu, on this I cannot see the option to change theme for these pages. Is there anyway to add it to this area? Or a way I can add the code anywhere to make it work for these too?

https://ww.wp.xz.cn/plugins/jonradio-multiple-themes/