Kane has scored twice in the tournament but has looked out of sorts, lacking pace and short on chances, prompting calls for him to be dropped for Wednesday's semi-final against Netherlands in Dortmund.
Alexander-Arnold, however, backed Kane and said England's all-time top scorer could create chances from nothing.
"Anyone who is facing England would like to see Harry Kane not playing," he said.
"You just know he is a threat. Anything in and around the box, you need to be on red alert.
"He can finish it from every angle. I always say he is the best finisher I've seen or played with. He can drop down and build play up and his hold-up play is incredible too."
England's attacking line has spluttered at the tournament, with Jude Bellingham and Phil Foden showing only flashes of their club form and their usual penetrating runs into the box have been lacking.
Bukayo Saka was more like himself in the quarter-final win over Switzerland and scored a superb leveller to take the game to extra time and penalties, but he showed reluctance to use his pace to run at defenders who had struggled to contain him.
No frustration
The Dutch, in contrast, have looked dangerous, in particular the tournament's joint-top scorer Cody Gakpo, although he faces a solid England defence that has conceded only three goals.
The Netherlands have looked shaky defensively, offering opportunities England can exploit if they can rediscover their attacking spark.
Left back Shaw, who returned from injury late in the Switzerland game, said Kane was a world-class player.
"At any time he can score a goal and make that difference. He's a very important player, he's our captain," Shaw said.
"You give him time in and around the box he'll score, he takes opportunities we know that, we see it day in day out, we know the quality he has and what he brings to the team and it's very important he's on the pitch."
Shaw said Kane had the right mindset despite his performances.
"I don't sense any frustration from him, he's the same Harry that we have from the start of the camp, nothing changed," he said.
"He'd have liked to have scored more goals. Nothing changed, he's still very positive... he's our captain, he's our leader, he leads by example and we all follow him."
