基本的には、前にやった手順で行けた。違いは各パッケージのバージョンが新しくなったくらい。

1. apache

$ sudo apt install apache2
$ apache2 -v
Server version: Apache/2.4.41 (Ubuntu)
Server built:   2020-04-13T17:19:17
$ systemctl status apache2
● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2020-05-06 19:00:17 JST; 1min 24s ago
       Docs: https://httpd.apache.org/docs/2.4/
   Main PID: 48243 (apache2)
      Tasks: 55 (limit: 19043)
     Memory: 6.2M
     CGroup: /system.slice/apache2.service
             ├─48243 /usr/sbin/apache2 -k start
             ├─48246 /usr/sbin/apache2 -k start
             └─48247 /usr/sbin/apache2 -k start

2. MariaDB

$ sudo apt install mariadb-server
$ sudo vi /etc/mysql/mariadb.conf.d/50-server.cnf
----
#character-set-server  = utf8mb4 
character-set-server  = utf8  # コチラに変更
#collation-server      = utf8mb4_general_ci  # コメント化
----
$ sudo systemctl restart mariadb
$ sudo mysql_secure_installation
（省略）

3. PHP

$ sudo apt install php php-mysql libapache2-mod-php
$ php -v
PHP 7.4.3 (cli) (built: Mar 26 2020 20:24:23) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies
    with Zend OPcache v7.4.3, Copyright (c), by Zend Technologies

4. phpMyAdmin

$ sudo apt install phpmyadmin