It seems like only yesterday Sombr was supposed to play the itty-bitty basement room at the Crocodile. That Seattle show never actually happened — at least not inside a small club.

As the alt-pop singer’s career skyrocketed last year with the inescapable megahit “Back to Friends,” organizers kept bumping the show to larger venues, ultimately going from the 300-capacity room to WAMU Theater — the last rung on the ladder before arenas. Less than a year later, the singer-songwriter born Shane Michael Boose is taking that final step into pop’s big leagues with his maiden arena tour, which began this week in Vancouver, B.C. Thursday’s stop at Climate Pledge Arena was the first U.S. date on the “You Are the Reason Tour,” and late into his 93-minute set, Sombr decided to have some fun with the increasingly large crowd he now commands.

The 21-year-old New Yorker had his crew flip the venue lights on so he could get a look at the crowd, an intergenerational mix indicative of the various touchstones in his songs that blend pop with early 2010s indie rock. Giddy as a kid at a Yankees game, Sombr started the wave through the arena, with the crowd’s commitment visibly tickling the young star who eventually had to tell them when to quit.

“All right guys, it’s time to get (expletive) depressed,” he said gleefully before booming through an extended “Back to Friends,” aka “the song that brought us all together.”

It felt like a genuine guard-down moment in a set woven with contrived arena-show bits that didn’t always land, as Sombr is understandably still finding his footing onstage.

Sonically, however, the artist who started out crafting heartachey songs in his Lower East Side bedroom had no problem retrofitting some of them for arenas. Most notably, the spare “Would’ve Been You” blossomed into a massive, if abbreviated, rock anthem with the help of his crack backing band. They similarly turned the gliding, disco-rock hit “Homewrecker” into a fizzier, more muscular ripper, with Sombr throwing a hint of pop-punk vocals into its squeaky clean chorus.

After some of his earliest singles presented Sombr as a young master of melancholic bedroom pop, he leaned into his glossier indie rock influences on last year’s “I Barely Know Her,” evoking artists like Foster the People and even his fellow New Yorkers, The Strokes. Sombr’s debut album retained his introverted intimacy while giving newfound fans something they could cry or groove to, often at the same time. Thanks to his knack for big, incredibly catchy hooks, Sombr’s music has landed at alternative and Top 40 radio stations alike, highlighting a subtle pull and tug between two worlds early in his career.

The Grammys best new artist nominee is widely considered among a wave of new pop stars, which may have contributed to Sombr being miscast for a George Michael tribute at last weekend’s MTV Video Music Awards. (Keep him on speed dial for any “This Is It” 30th anniversary salutes, however.)

It shouldn’t be surprising that an artist with limited big-stage reps and a still-growing catalog of insular songs isn’t the most charismatic performer at this point in his nascent career. Sombr’s stage presence often felt stiff, particularly during some scripted crowd work and for-the-cameras histrionics — including an awkward tongue-wagging close-up that looked uncomfortable for everyone involved. Elsewhere, a prerecorded video segment meant to highlight Sombr’s connection with his fans was so over the top that it blurred the line between genuine gratitude and stan-cultivating propaganda. 

But when his power-washed music hit, Sombr capably worked the large stage, done up like a graffitied New York City street that resembled a Broadway “Rent” production on steroids.

Most importantly, Sombr showed confidence in his vocals, largely eschewing the heavy reverb deployed throughout “I Barely Know Her,” delivering them with a more crystalline force instead. The strength of his voice was best displayed on his poignant new single, “My Body Isn’t Ready,” a power ballad tackling his own body image issues. Two songs later, he took a more musically playful turn on similarly intimate themes during “Undressed,” a certified bop that could slot on a playlist alongside major label “indie” bands like Franz Ferdinand or The Bravery.

By the end of the night, Sombr was at his loosest during a double shot of “12 to 12,” running the disco rocker back for a second time to cap the night. “I wouldn’t normally do this,” he said of the move he pulled two nights earlier at the tour’s opening night. Not that anyone seemed to mind the confetti-doused rerun.