This is a question we get the most often through the support tickets. When the Pi foundation brought out the Raspberry Pi 4, they swapped one of the Dual Stack USBs and the ethernet port, which allowed them to add USB 3.0 but limited us.
We’ve had users send us messages on social media show how they’ve got their pi-top1 and pi-topCEED working with the Raspberry Pi 4 (Kudos to the maker community for being awesome as always ). They’ve usually backpowerd the Raspberry Pi through their 40pin connector and then grabbed a microHDMI - HDMI adapter et voila!
The pi-top unfortuantely has some mechanical issues, the HDMI port gets in the way of connecting a microHDMI device through to the pi-top Hub and the Ethernet port gets in the way of connecting the USB ports to our keyboard and internal USB Port. All of this means we would need to do a redesign of our pi-top  Hardware which costs a lot of money. We’re aware of how frustarting this is for those of you that helped support us during the pi-top days. Though for the moment, the Raspberry Pi 4 cannot go into the pi-top.