As I wrote recently, a new edition of my Object Pascal Handbook updated for Delphi 10.4. Sydney is in the works. The current version (very close to final) has now been made available by Embarcadero, with no particular restriction save for providing contact information in the download form:

https://lp.embarcadero.com/Object-Pascal-Handbook-2021

I'm still working on the finishing touches of the printed version, which I expect to be available in January 2021.