Interesting. How many % he could improve? Any speed would be crucial
Depends on the person but it is pretty clear Garcia is not in the best physical shape he could be at all. He looks 'skinny-fat'. The fact he weighs 76kg (only a few off Araujo, who's like 4 inches taller) tells you it all, probably much more of that is fat then it should be, as you can see https://www.youtube.com/watch?v=7sGv2dfTNRo
Most of the fastest players are in amazing shape and ripped af e.g Haaland, Adama, Sane, Davies. So yes if Garcia could get in great shape and get more muscular to add power you can assume he will get reasonably faster.
But a lot of players just never end up doing so like the amigos in the last few years.