open your terminal in Ubuntu 18.04 or 20.04 Desktop

$ sudo apt update

(If you open a fresh terminal tab. Enter your Ubuntu Desktop sudo user password)

Desktop@Sondria46.info :~$ sudo apt update

[sudo] password for Desktop: 

Hit:1 https://dl.google.com/linux/chrome/deb stable InRelease

Get:2 http://security.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]    

Hit:3 http://in.archive.ubuntu.com/ubuntu bionic InRelease                     

Hit:4 http://ppa.launchpad.net/gerardpuig/ppa/ubuntu bionic InRelease          

Get:5 http://in.archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]   

Hit:6 http://ppa.launchpad.net/maarten-fonville/android-studio/ubuntu bionic InRelease

Get:7 http://in.archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB] 

Fetched 252 kB in 2s (129 kB/s)    

Reading package lists... Done

Building dependency tree       

Reading state information... Done

All packages are up to date.

$ sudo apt install apache2

Desktop@Sondria46.info:~$ sudo apt install apache2

Reading package lists... Done

Building dependency tree       

Reading state information... Done

Suggested packages:

  apache2-doc apache2-suexec-pristine | apache2-suexec-custom

The following NEW packages will be installed:

  apache2

0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.

Need to get 95.1 kB of archives.

After this operation, 537 kB of additional disk space will be used.

Get:1 http://in.archive.ubuntu.com/ubuntu bionic-updates/main amd64 apache2 amd64 2.4.29-1ubuntu4.25 [95.1 kB]

Fetched 95.1 kB in 1s (106 kB/s) 

Selecting previously unselected package apache2.

(Reading database ... 165245 files and directories currently installed.)

Preparing to unpack .../apache2_2.4.29-1ubuntu4.25_amd64.deb ...

Unpacking apache2 (2.4.29-1ubuntu4.25) ...

Setting up apache2 (2.4.29-1ubuntu4.25) ...

Processing triggers for systemd (237-3ubuntu10.53) ...

Processing triggers for man-db (2.8.3-2ubuntu0.1) ...

Processing triggers for ufw (0.36-0ubuntu0.18.04.2) ...

Processing triggers for ureadahead (0.100.0-21) ...

ureadahead will be reprofiled on next reboot

You can check Apache2 is installed or not in your ubuntu Desktop 

$ whereis apache2

Desktop@Sondria46.info:~$ whereis apache2

apache2: /usr/sbin/apache2 /usr/lib/apache2 /etc/apache2 /usr/share/apache2 /usr/share/man/man8/apache2.8.gz

Now you can know apache2 version

$ apache2 -v

Desktop@Sondria46.info:~$ apache2 -v
Server version: Apache/2.4.29 (Ubuntu)
Server built:   2022-06-23T12:51:37

that's it...