It can be lonely being a protagonist. You go about your day with all kinds of terrible things happening to you, and there's not always someone to talk to about it. But protags need friends and confidants. And not just because it's lonely.
It's difficult to write a character who has no one to talk to.
Solitary protag stories are hard to write. The protag is in their head all the time, internalizing, talking to themselves. Some of this is great (you really get to know a protag that way), but too much and your reader can wind up telling your protag to zip it and get on with things.
Sidekicks and secondary characters are there to help keep your protag out of their head. They're perfect for getting information across to your reader in logical and natural ways. They provide ways to look at the other side of an issue, to help guide your protag to a revelation they need to make. They can be the balance your protag needs. Or the bad influence.
Interaction with other characters -- no matter how minor -- also helps dramatize scenes that would otherwise be told.
Bob stopped at the gas station as asked the attendant what was with all the army trucks. He said with the army, it had to be something.Bor-ing. Do you get any sense that this matters? Any tension? It's a missed opportunity.
Bob got out of the car and swiped his credit card at the pump. A convoy of army trucks rumbled by, stirring up dust. The gas station attendant just shook his head as they passed.Better, right? A small scene, but there's a sense that something is happening, trouble is brewing. Later, Bob might see another small detail and start putting things together.
"Been like that all day," he said. "One right after the other."
Bob stuck the nozzle in the tank. "Something going on?"
"It's the army. Something's always going on with them."
If you have a scene that feels heavy and bogged down with too much internalization or description (or even a summarized or told section like the example), look for ways you can add a person for your protag to interact with. It doesn't even have to be a person. Animals work fine, too, or even talking out loud to themselves. (Though be careful with this, as you don't want them to look like a idiot and it can start to feel fake after a while). Even minor exchanges can add depth and flavor and allow you to show, not tell. It's a win/win.
By our natures, we like to watch how other people interact. And stories are just a bunch of people interacting.