[mysql] ERROR 1698 (28000): Access denied for user 'root'@'localhost'

There is a good and regularly updated guide on how to set a new password for the latest MySQL.

https://www.digitalocean.com/community/tutorials/how-to-install-mysql-on-ubuntu-20-04

It would be best to read whole topic from the link above but in short, this maybe could help,

Run the security script:

sudo mysql_secure_installation

Detailed Info for "mysql_secure_installation"

After that, you can change password by following the next steps

sudo mysql

mysql> ALTER USER 'root'@'localhost' IDENTIFIED WITH caching_sha2_password BY 'password';

Detailed Info for changin root user password

If you have a problem maybe you will need to reinstall MySql.