Thank you for reaching out and sorry to hear you are facing trouble using Adobe XD. as of now we don't have any shortcut to close the Property inspect (PI) section and as this PI has all the options to help developer or designers or anyone who uses XD, this has been disabled intentionally and you can raise feature request here.
Hi, there should be a possibility to temporary hide/show control panels like it is in Photoshop by just pressing Tab, for better quick view (besides preview mode in new tab)