I write in third person limited, meaning my narrator knows the thoughts and feelings of only one character in the book (the hero). Everybody is still referred to as "he", "she", "they", etc, (never "I"), but the narrator does not reveal anything the hero does not plausibly know or see.
My latest hero often encounters strangers on her quest and interacts with them, without names.
My solution for the narration is to temporarily pick some unique characteristic she (and the narrator) uses to refer to them, but if they use a name in conversation (as people do) start using the name.
IRL, you learn the names of your friends, enemies, coworkers and store clerks eventually, somehow. Once I know a character is going to be important later, I typically "engineer" one of these ways into a first encounter. In this segment, my female hero is seeking passage on a primitive down river barge:
As she approached the next station, she saw just the type of barge she was looking for: No animals, and the cargo looked like simple lumber and some barrels. A man in his forties was tilting barrels, apparently heavy with something, and rolling them toward the pilot house.
"Sir?" she called, still walking toward him. He stopped and looked up, squinting, waiting for her to get closer.
"Do you take passengers?" Alice asked. "I aim to get to Corktown."
The barrel-man turned and called to the pilot house. "Brady! Yo! Do you want a passenger?" He turned back to Alice who had reached the end of the barge. "Give him a minute," he said, and began rolling his barrel again.
When Brady emerges, he is called by name. Note that if I had put Brady on the barge rolling barrels, it would have been a bit more awkward for Alice to learn his name, since (as in real life) they likely would conclude their transaction first without names. I would introduce "barrel man" as an 'extra' doing some labor for Brady that we don't really need to see again. Without the barrel man, It would need to be a more explicit exchange. Say after a price was agreed:
"Done then," he said, pocketing the cash. "What's your name?"
"Alice," he repeated, and pointed at himself. "Brady. I leave at noon, with or without you."
Like names, "barrel man" here would not be used every time, just about as often as I use any other name. That IS his name in Alice's mind. Likewise in another situation, speaking to three clerks, she might use "bald clerk", "tall clerk" and "young clerk". Some salient detail she has plausibly noticed that would separate the people for the reader. If a name is learned, it is used thereafter:
The bald clerk rolled his eyes, and addressed the young clerk. "David? Would you please shut up?"
David was going to respond, but seeing the stern look in the bald clerk's eyes, clamped his mouth shut.
If the "barrel man" above reappears later, but is not important enough to name, he remains "barrel man", whether barrels are present or not.
But eventually, like in real life, your character(s) need to learn the names of other characters. I favor indirect approaches like above, Brady and David can be important later in the story. Or callouts:
"See that guy? Red tie? Sam Philbin, the weather guy."
"Alice, this is Jerry, the runner I told you about."
Whatever real-life tricks you can imagine. As a last resort, in real life, we can resort to direct query:
"Hi, I'm Alice," she said, extending a hand.
The boy took it. "Griffy," he said, "It's Griffin really, after my grandfather, but everyone calls me Griffy. Except my mother. And my sister, she thinks my name is 'dumbass'."
For myself, I would not refer to any character by a label or title for more than a single scene (which may be a whole chapter). If I were referring to them for two or more scenes, I engineer some way for my hero to learn their name, preferably indirectly. For dramatic effect, I often use direct introduction for "important" characters that will be an ongoing presence. Of course for friends and family, I do the opposite of the above from the heroes POV: The hero uses the name mentally, but the reader has to learn their role. So
Her mother shouted from the kitchen. "Bill? Where are you?"
Her father shouted from the garage, not in anger but for volume, "I'm busy!"
Somehow or another we have all learned the names of hundreds of people. Try to employ in writing all the ways that can happen in real life.
He walked into the office, there was only one blonde woman at the desks, so he approached her.
"Hi, are you Alice?"
"Yes," she said, still reading her computer screen, then looked to him. "How can I help you?"
"I'm David, from engineering. I was told you handle ordering for machine parts?"
You can find thousands of name suggestions online, particularly looking for baby names. Personally I try to avoid duplicates and keep a list in alphabetic order for characters in the story. If I need new characters, I look for a first letter I haven't used before, at least for that gender. If I don't like any of them, I will reuse a letter, but make sure the names read and sound distinct enough for the reader to keep them straight. Not "Billy" and "Bailey", maybe "Billy" and "Brad", or "Burke".