accept command line argument

[snippsat]

without using global keyboard.
files = Path.cwd().glob(f"*{coll}*") just for learning purpose.

Hmm global keyboard? maybe you meant global keyword.
It not a global keyword and it's ok to use like this.
Path.glob a trick it to make make it recursively is to add **.

files = Path.cwd().glob(f"**/{coll}*")

@app.command() what this line mean

It's a decorator this mean that can get a clean interface and hide all code that needed in background.
The author of Typer is also author of FastAPI where you see same decorator pattern.
Flask was one the library's first that used this way pattern a lot.
Flask

from flask import Flask

app = Flask(__name__)

@app.route("/")
def hello_world():
    return "<p>Hello, World!</p>"

FastAPI

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"Hello": "World"}

Typer.

import typer

app = typer.Typer()

@app.command()
def hello(name: str):
    print(f"Hello {name}")