Kali linux does not update and does not upgrade

Kali Linux has some problems, can you help me in detail to solve these problems? I am using Kali Linux version 2020.2.

1. I write sudo apt update and sudo apt upgrade, it doesn't update and doesn't upgrade. Reading package list... Done All packages up to date. He gives it as an Output. So there are no updates and upgrades.

2. I want to download and install virtualbox through the terminal. For this, I type sudo apt install virtualbox or sudo apt install virtualbox -y in Terminal, but it gives an error. Virtualbox-7.0 Debian-bullseye [Not candidate version] E: Package 'virtualbox' has no installation candidate. I'm trying so hard to solve these errors, I'm looking on the internet. But it doesn't work. sudo nano /etc/apt/sources.list This file is empty.