Why can’t the US president drive, officially? Or is it not official? What steps could be taken to allow this action.
Legally, nothing prevents the U.S. president from performing ordinary activities.
In practice, U.S. presidents try to avoid doing things (like driving) that make it harder for the Secret Service to protect the president. But if a president insists on doing something (such as riding a horse on a remote ranch, or cutting brush with a chainsaw on a large ranch), the Secret Service will accommodate him. Where possible, arrangements will be made so that the president can perform his hobby (such as jogging) in a securable location (such as a custom-built White House jogging track, or a university athletic field). The Secret Service will even arrange for its agents to be trained in a hobby (such as horse-back riding) to be able to provide the best possible support for the president.
Also, there are benefits to a president from letting someone else drive. He can read through notes, make telephone calls, or sit back and relax. The driver will be a professional who knows how to handle a variety of emergency situations. Also, the driver can handle any worries about making the route unpredictable.
@Jasper's answer does a good job of explaining, but just to mention that the "no driving" rule also applies to Ex-Presidents.
That's because current and former presidents and vice presidents are not allowed to operate motor vehicles on the open road.
For security reasons, high profile government officials and former officials, like Barack Obama and Joe Biden, as well as both Bill and Hillary Clinton, have to rely on their appointed secret service teams, who are trained in "evasive and defensive driving maneuvers."
The assassination of John F. Kennedy in 1963 was a turning point in this lifetime security requirement. Lyndon Johnson was the last president to drive on public roads.
Though the rule is not law, it's highly enforced by the secret service and all parties seem to adhere.
And a blurb from BBC
...US presidents and former presidents are not allowed to drive on public roads...
And miscellaneous quotes from current and former Presidents and Vice-Presidents:
Bush, 67, whose main residence now is in Dallas, auctioned the 2009 Ford F-150 King Ranch 4x4 SuperCrew for charity for $300,000 in January, saying in a statement that he hadn't driven on a public road for "many, many years." ...
Biden, 71, hasn't given up completely on the idea that he'll one day drive again. He owns a 1967 Chevrolet Corvette, a green convertible with a 327-cubic-inch engine and side exhaust pipes. He told "Car and Driver" magazine in 2011 that being banned from driving is "the one thing I hate about this job." ...
"One of the regrets I have about public life is that I can't drive anymore," Hillary Clinton told the National Automobile Dealers Association in January. Bill Clinton has shared the same sentiment.
As BruceWayne points out, there's no law preventing the president from driving. It's just a really bad idea. If you watch the Zapruder film, you'll see why anybody driving the president needs split-second response times. JFK's armored car appears to slow down momentarily after the first shot is fired, which kept the president in the line of fire. Watch the Reagan shooting tape if you want to see how much the Secret Service improved in a few years. Every single agent knew exactly what to do, including throwing Reagan in the limo and driving fast to GW Hospital.
Another reason to keep "important" people from driving is to keep them from having car accidents. In February 1977, Rene Levesque, then premier of the province of Quebec (in Canada) was driving home from a late night poker game. He hit a homeless person on the road, killing him. That was the last time a Quebec premier was allowed to drive.
Ref: https://beverlyakerman.blogspot.com/2012/11/quebec-corruption-lets-not-forget-rene.html The best quote from that posting:
"Quebec is the only place in the world where it is the victim who is given the blood test," a former provincial Liberal minister dryly commented.