The fallen Jedi Darth Vader can perform incredible feats with the dark side of the Force, but Grand Moff Tarkin learned before A New Hope there's actually a limit to the Sith Lord's powers.
Tarkin makes the stunning discovery during an equally as unexpected mission in 2017's Darth Vader #18 by writer Charles Soule, penciller and artist Giuseppe Camuncoli, inker Daniele Orlandini, colorist David Curiel and letterer Joe Caramagna. Darth Vader, who had earlier performed a favor for Tarkin when subduing the rebellious Mon Calamari, decides to cash in on his superior's debt by requesting that Tarkin hunt him on Tarkin's home planet of Eriadu to see if he could still be challenged in a Galaxy devoid of Jedi.
During the odd excursion, Tarkin sacrifices members of his hunting party to learn Vader's weaknesses and discovers that Vader's deadly precision with the Force has a limited range. Although Tarkin never discloses the actual distance he must maintain in order to avoid getting Force Choked to death, he isn't that far from Vader once he divulges the truth and doesn't die, so it can be assumed that he's out of Vader's range during this time. Based on the drawings, a fair guesstimate would be that Vader's range is mere meters.
Of course, this isn't to say that Vader can't wield the Force from great distances. He just needs to be closer to his prey to kill them with the Force. Star Wars proves this earlier when Vader attempts to kill one of the few remaining Jedi, Kirak Infil'a, to obtain his lightsaber. When he first lays eyes on Kirak, Vader is standing at the bottom of a massive dam while Kirak peers down from a high mountain. Vader successfully Force Chokes the Jedi from this distance but fails to finish the job as Kirak quickly breaks Vader's hold. It can therefore be assumed that part of the reason why Vader fails to finish off Kirak this way, aside from the Jedi's strong connection to the Force, is the distance between them.
Vader has proven he's capable of channeling the Force to manipulate faraway objects. In 2020's Darth Vader series that transpires after The Empire Strikes Back, the Sith Lord not only survives a rigged explosion on the Hutt Clans' capital ship but uses the Force to build a space pod from the debris, a rudimentary design that withstands the friction when entering the atmosphere of the nearby planet Jekara and the subsequent impact with the planet's surface. Earlier in that same series, Vader also tames the Red Horror, a subspecies of the Summa-Verminoth that's so large that successfully controlling such a creature would undoubtedly require pushing the Force quite far, much further than a few meters.
Although Vader can only kill with the Force when in close proximity to his target, he is still capable of wielding the Force effectively in other capacities at great distances. Writers created this limitation as a way to put some handicaps on the Sith Lord so that he isn't overly powerful. A Darth Vader that can successfully kill his prey with a Force Choke at any distance could potentially end the lives of people on other planets with a thought. That said, him possessing this capability and refusing to utilize it would have added to his character. In fact, there are plenty of examples in Star Wars where Force wielders voluntarily choose not to wield the Force in certain ways. For instance, Sith don't employ Jedi mind tricks because they prefer a more direct approach to obtaining information such as torture. There's also the fact that Force-wielders prefer fighting in close proximity with their opponents, hence why many prefer the use of lightsabers. Unfortunately, writers didn't choose a similar path for Darth Vader in this instance.