since the latest update on ubuntu the save as box looks like an old microsoft office save as box and I can,t save to my usb stick
Oh - you seem to mix 2 problems. Your “ancient” user interface look (problem 1) is due to a missing GTK3 support package (but I’d expect your complete LibreOffice looks like that, not file picker dialog only), while a missing USB integration (problem 2) got nothing to do with LibreOffice, but may be a problem of your system.
GTK3 package problem
Execute sudo apt install libreoffice-gtk3 to install the required package.