My website is unable to connect to mysql database after ubuntu upgrade from 16.04 to 20.04

Hi team, please i need your assistance – I just upgraded from Ubuntu 16.04 to 20.04 - now my application is unable to connect to the mysql database.
I get this error on the frontpage of my website — "Error: Call to a member function getActive() on null: Could not connect to MySQL server"

Then I tried to restore backup - this also resulted in error for mysql backup restore
ERROR 1062 (23000) at line 5530 in file: ‘/tmp/.webmin/169494_25704_1_restore.cgi/martfame.com_mysql_martfame_jmln1’: Duplicate entry ‘’ for key 'uh46v_finder_terms.idx_term’

Operating system:
Ubuntu
OS version:
20.04

Just to provide extra information – this is what I have in mysql.cnf file

The MySQL database server configuration file.

One can use all long options that the program supports.

Run program with --help to get a list of available options and with

–print-defaults to see which it would actually understand and use.

For explanations see

MySQL :: MySQL 8.0 Reference Manual :: 5.1.8 Server System Variables

Here is entries for some specific programs

The following values assume you have at least 32M ram

[mysqld]

* Basic Settings

user = mysql

pid-file = /var/run/mysqld/mysqld.pid

socket = /var/run/mysqld/mysqld.sock

port = 3306

datadir = /var/lib/mysql

If MySQL is running as a replication slave, this should be

changed. Ref MySQL :: MySQL 8.0 Reference Manual :: 5.1.8 Server System Variables

tmpdir = /tmp

Instead of skip-networking the default is now to listen only on

localhost which is more compatible and is not less secure.

bind-address = 127.0.0.1
mysqlx-bind-address = 127.0.0.1

* Fine Tuning

key_buffer_size = 16M
max_allowed_packet = 512M

thread_stack = 256K

thread_cache_size = -1

This replaces the startup script and checks MyISAM tables if needed

the first time they are touched

myisam-recover-options = BACKUP

max_connections = 151

table_open_cache = 4000

* Logging and Replication

Both location gets rotated by the cronjob.

Log all queries

Be aware that this log type is a performance killer.

general_log_file = /var/log/mysql/query.log

general_log = 1

Error log - should be very few entries.

log_error = /var/log/mysql/error.log

Here you can see queries with especially long duration

slow_query_log = 1

slow_query_log_file = /var/log/mysql/mysql-slow.log

long_query_time = 2

log-queries-not-using-indexes

The following can be used as easy to replay backup logs or for replication.

note: if you are setting up a replication slave, see README.Debian about

other settings you may need to change.

server-id = 1

log_bin = /var/log/mysql/mysql-bin.log

binlog_expire_logs_seconds = 2592000

max_binlog_size = 100M

binlog_do_db = include_database_name

binlog_ignore_db = include_database_name