I don’t have the Ubuntu software center on 20.4

It really should not matter if you are running Ubuntu in a Virtual Machine. Although I have no knowledge of Ṕarallels’, I think the software center should be there.

Seeing this video https://www.google.com/search?client=firefox-b-d&q=install+ubuntu+in+parallels#kpvalbx=_fPJnYtHQLNSDur4PzqKAoAc13 (it is on youtube), I see that it is more limited though. Might be that is due to being the ARM version.

Look what software is installed. And then use the command-line (terminal).

Install

You can install Ubuntu Software like so:

sudo apt install ubuntu-software

or install Gnome Software in newer releases of Ubuntu like so:

sudo apt install gnome-software

Reinstall

You can reinstall Ubuntu Software like so:

sudo apt install --reinstall ubuntu-software

or reinstall Gnome Software in newer releases of Ubuntu like so:

sudo apt install --reinstall gnome-software

Reset

You can reset Ubuntu Software to its vanilla settings.

First, purge it like so:

sudo apt purge ubuntu-software

Then, install it like so:

sudo apt install ubuntu-software

or reset Gnome Software in newer releases of Ubuntu.

First, purge it like so:

sudo apt purge gnome-software

Then, install it like so:

sudo apt install gnome-software

It works the same for Zoom.

Sudo apt install zoom