Решение

import s_taper
from s_taper.consts import *

scheme = {
    "userid": INT + KEY,
    "inv": TEXT
}

players = s_taper.Taper("players", "data.db").create_table(scheme)

def check_inv(player: int):
    inv = players.read("userid", player)
    text = f"Инвентарь:\n"
    inv = inv[1]
    for name, amount in inv.items():
        text += f"{name}: {amount}\n"
    print(text)


def add_item_to_inv(player: int, item: tuple[str, int]):
    data = players.read("userid", player)
    inv = data[1]
    inv[item[0]] = item[1]
    players.write([player, inv])


if __name__ == '__main__':
    while True:
        if input("mode: ") == "1":
            userid = int(input("Enter userid: "))
            check_inv(userid)
        else:
            userid = int(input("Enter userid: "))
            name = input("Enter item name: ")
            amount = int(input("Enter amount: "))
            add_item_to_inv(userid, (name, amount))