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Remarks:

• Bug: random.randint(0,len(numbers)) should be random.randint(0, len(numbers) - 1) since the end is inclusive. If you run your program enough it gives an IndexError.
• Avoid indexing--prefer random.choices to select random items from a list (random.choice if you just want to select one item).
• Separate user interaction (I/O) and algorithm logic.
• Use a function to make your code reusable, testable and abstract away complexity.
• Add type hints to your function and check them with pyright.
• Don't use f-strings unless there's actually interpolation happening.
• Don't assume input is valid; handle errors gracefully.
• There is no performance issue with your code, so "optimization" doesn't matter at this point. Focus on coding style and writing maintainable code.
• Add docstrings.
• Consider adding unit tests. Since your code uses randomness, you can use a regex or logic to make sure the password has the right stuff in it, or seed the random library to be deterministic. You could find your crash mentioned above using a fuzz test--run thousands of random inputs.

Here's a rewrite:

from random import choices, shuffle
from string import ascii_letters


def generate_password(nr_letters: int, nr_numbers: int, nr_symbols: int) -> str:
    """Generates a password with n random letters, numbers and symbols"""
    numbers = "0123456789"
    symbols = "!#$%&()*+"
    password = [
        *choices(ascii_letters, k=nr_letters),
        *choices(numbers, k=nr_numbers),
        *choices(symbols, k=nr_symbols),
    ]
    shuffle(password)
    return "".join(password)


def read_positive_int(
    prompt: str, invalid: str = "Input must be a positive integer"
) -> int:
    """Reads a positive integer input from stdin, repeating until successful"""
    while True:
        try:
            if (n := int(input(prompt))) > 0:
                return n
        except ValueError:
            ...
        print(invalid)


def main():
    """Interacts with the user to generate a password"""
    print("Welcome to the PyPassword Generator!")
    nr_letters = read_positive_int("How many letters would you like in your password? ")
    nr_symbols = read_positive_int("How many symbols would you like? ")
    nr_numbers = read_positive_int("How many numbers would you like? ")
    password = generate_password(nr_letters, nr_numbers, nr_symbols)
    print(password)


if __name__ == "__main__":
    main()

You could generalize this a step further and accept arbitrary iterables and counts instead of hardcoded letters, numbers and symbols, but that seems a bit premature, so I left the function as-is in that respect.

3 positional args is getting to be a bit much, so you might want to make those kwargs as well, also left as a future improvement.