I transited through Beijing in 2018 and 2020 en route to Aus/NZ. Both times we stayed in the Airport Hilton, which I would recommend for a day or two layover. On the first transit we stayed two nights and booked a guide and car for the day. Hotel pick-up, out to the Great Wall before the crowds, which worked perfectly, then Tainanmen Sq & Forbidden City. It was great. Happy to dig out details. Second time we had something like 15hrs so just booked a half-day rate at the hotel, which got us a room from 8am-6pm or something, plus Club Lounge access.