Forest loss data is available for the study period (2000 - 2020). I've worked with this specific data source quite a bit. While it's known for being the gold standard in global forest loss estimation there are many countries that criticize it for over estimating loss. Going back further than 1985 is difficult/impossible as the estimate is derived from satellite data.
I'm not thinking of early satellites, but rather spy planes like the U-2 and SR-71 (and their equivalents in other countries). They would take use big long reels of physical film, covering quite broad areas on continuous capture from high altitude. It's possible that much was discarded but my guess is that most of it was archived somewhere for the intelligence community. (I'm sure that some areas of the world got more attention than others, of course).
I wonder if declassified cold war spy plane photos might be usable to extend the records farther back in history? The resolution and coverage should be pretty good.