One option would be to drop $50 on PHP if you don't already have one, take a sharpie and strike out "D&D" on the top, and write "BG3" in its place. Then, as you encounter the homebrew changes, just annotate your PHB with the change. A little more $$$ and work up front, but eventually, you'll have a printed manual.
This is only maybe 50% tongue-in-cheek. Annotating something that's already 50% or more what you want isn't the worst option if the other options aren't palatable.
... and then in 2 years when they make a small change in an update, you can annotate the annotations ...
