By Suzanne Kapner 

The Covid-19 pandemic didn't just change consumer habits. It also prompted retailers to rethink Black Friday, one of the biggest shopping days of the year.

Many stores stayed closed this Thanksgiving, in a break with a pre-pandemic tradition of opening Thursday evening. Retailers have moved away from doorbusters, the deeply discounted items available for a limited time that drew hordes of shoppers to stores on Friday morning. Instead, they have been dangling Black Friday deals all month, both online and in stores. Some hosted streaming events on their websites on Friday as an alternative to visiting a store.

"Customers are shopping differently this year," said Greg Revelle, Kohl's Corp.'s chief marketing officer. "We had to alter our Black Friday strategy."

Stores are trying to balance what forecasters predict will be record holiday sales with supply-chain constraints that have kept some items in short supply.

Black Friday shoppers spent $6.6 billion online as of 9 p.m. ET, according to Adobe Inc. Adobe estimates that when the final tally is in, consumers will have spent between $8.8 billion and $9.2 billion online, compared with $9.03 billion a year ago.

Many consumers were able to save money during the pandemic and are now spending freely despite rising inflation. That bodes well for the holiday season, executives and analysts said.

The National Retail Federation expects sales during November and December to rise by a record 8.5% to 10.5% to as much as $859 billion, compared with a year ago. That is in contrast to an average increase of 4.4% over the past five years. The forecast was made before the World Health Organization declared Friday that a new strain of the coronavirus, first detected in southern Africa, was a global "variant of concern." The move triggered worries that travel restrictions and other curbs would spoil the global economy's recovery.

The trade group predicts that nearly 2 million more people, or a total of 158.3 million, will shop over Thanksgiving weekend this year, compared with last year. Still, that is down from the 165.3 million people who shopped over the same weekend in 2019, before the pandemic.

John Rulli, chief administrative officer for mall owner Simon Property Group, said on Friday afternoon that foot traffic was exceeding 2019 levels at a number of its shopping centers, particularly in the New York-New Jersey metropolitan area and Atlanta. Other areas such as Boston started out a bit slower, Mr. Rulli said. "Overall, we're off to a good start," he said.

As vaccines become widely available and Covid-19-related restrictions are eased, people have been returning to concerts, the movies and traveling. For many, shopping in stores on Black Friday is a social ritual they are eager to resume.

Last year, Andrew Lubera paused his tradition of shopping in stores on Black Friday because of the pandemic.

This year he waited in the dark outside a Walmart in Catskill, N.Y., aiming to be one of the first shoppers inside when the store opened at 5 a.m. to snag toys. "Last year I didn't shop, but I want to get a few toys, maybe some clothes," said the 42-year-old as he waited with a few dozen eager shoppers.

His wife has already done most of their Christmas shopping online but asked him to head out for a few deals. "She's still home in bed," he said.

Concerns about out-of-stock items and potential shipping delays as well as Black Friday deals on offer since the beginning of November prompted consumers to shop earlier. Sixty-one percent of shoppers surveyed by the NRF said they had started their holiday shopping before Thanksgiving, up from 51% a decade ago.

Digital out-of-stock messages are up 261% in November compared with November 2019, according to Adobe Inc., a software company that tracks online shopping. Out-of-stock messages declined slightly on Thanksgiving compared with the previous Thursday, as retailers focused their marketing on in-stock items, Adobe said.

Shoppers spent $5.1 billion online on Thanksgiving, Adobe said, flat from a year ago, when Thanksgiving Day online spending set a record with many stores closed for the first time.

Andrew Diaz said he completed more than half of his holiday shopping before Thanksgiving. Worried about shipping delays, the 24-year-old said he plans to visit the mall near his Costa Mesa, Calif., home on Friday to purchase the rest of the items on his list. "I'm worried that if I wait, the stores will be out of stock," he said. "It doesn't seem like they have enough products."

While larger retailers such as Walmart Inc. and Target Corp. accelerated imports and chartered their own ships to sidestep supply-chain problems, some smaller chains, including Gap Inc., Victoria's Secret & Co. and Urban Outfitters Inc. are scrambling to keep their shelves stocked.

Delays caused by Covid-19 outbreaks that disrupted production in Asia and a surge of imports as retailers stocked for the holiday season have created a backlog of container ships waiting to enter Southern California ports. On Tuesday, Gap predicted supply-chain disruptions would result in about $550 million to $650 million in lost sales.

E-commerce sales surged last holiday season, while many nonessential retailers were either temporarily closed or had restricted capacity. This year, online sales for November and December are expected to total $207 billion, a 10% increase over 2020, according to Adobe. That is less than the 32% jump last year, compared with 2019. Some chains, including Best Buy Co. and Dick's Sporting Goods Inc., recently reported a slowdown in digital sales.

Visits to physical stores are picking up, but foot traffic is still below pre-pandemic levels. For the week ended Nov. 20, visits to physical stores were 12.4% below the same week in 2019, according to Sensormatic Solutions, which tracks footsteps with cameras placed at stores.

Brian Field, senior director of Sensormatic Solutions' retail consulting practice, said he expects traffic during this year's Black Friday week to fall from 2019 levels, but the drop won't be as steep as last year.

Many shoppers still came out for fun. "My grandson wants a VR headset," said Normandy Loftin, a 56-year-old pushing an empty cart through the Catskill Walmart Friday soon after the store's 5 a.m. opening. An hour later her cart was piled high with pink toy cars, scooters and other gifts for her grandchildren. "Grandma is done with Christmas!" she said.

Retailers are giving shoppers less reason to visit stores this Black Friday compared with prior years. The term doorbuster didn't appear in Black Friday advertisements this year at Walmart, Best Buy and other major retailers analyzed by online discount marketplace Brad's Deals.

Chains including Macy's Inc. and Saks Fifth Avenue held gift-themed streaming events on their websites on Black Friday. Singer-songwriter Malia hosted "The Best Black Friday Deals" on Macy's website. Saks's show featured La Mer skin-care products.

"People got comfortable communicating through digital platforms during Covid," said Emily Essner, Saks's chief marketing officer. "This is a customer behavior that has absolutely changed and is not going away."

Lana Hinds and her sister used to map out their Black Friday shopping plans on Thursday as soon as the turkey was cleared from the table. Then, they would get up early Friday morning to wait in line at big-box chains. This year, Ms. Hinds, who lives in Greenville, S.C., plans to do all her holiday shopping online.

"It's easier to shop from my home," the 35-year-old said. "I don't have to deal with the traffic, getting up early, or waiting in line."

Sarah Nassauer, Sharon Terlep and Charity L. Scott contributed to this article.

Write to Suzanne Kapner at Suzanne.Kapner@wsj.com