This is a very simple mod. It just sets the reach distance to a very large value.
This is the official fork from the original creator of the long-reach mod. It's now maintained on the mod portal again as well: https://mods.factorio.com/mod/long-reach
Do you ever find it annoying that you're not quite close enough to something to place it? Are you playing marathon mode and constantly running around your base refilling chests in the early game? Would you prefer Factorio to play more like an RTS? This mod is for you.
If this mod is active, you can reach basically anything you can see in the viewport. In fact, you can reach much further than that, but since you can't scroll that far, you won't.
You can change the reach distances in the mod settings page. By default, you can reach just about the maximally zoomed out viewport. You can change it to allow reaching much further (e.g. edit remote bases in zoomed-in map view).
Why data-final-fixes.lua? I don't know. data.lua didn't work. Maybe some other
mod was overriding the player prototype. This mod tries to take precedence
over all other mods that affect the reach distance. If you don't want that, this
mod is not for you.
Instructions are here: https://wiki.factorio.com/index.php?title=Installing_Mods