I'm not expert in Linux, but after soooo long I finally found a way to install Adobe Photoshop 6 on Ubuntu 20.04 (Focal Fossa). Why Adobe Photoshop 6? That's all I have.

Before we continue, I assume you already familiar on how to install application on Ubuntu. Also prepare lot of internet packet data, you'll need it.

1. Install Wine

$ sudo apt update

$ sudo apt install wine

2. Set up 32 bit Wine Environment

$ rm -rf ~/.wine

$ WINEARCH=win32 winecfg

3. Install winetricks

$ sudo apt install winetricks

4. Install depencencies for Adobe Photoshop 6

$ winetricks atmlib gdiplus msxml3 msxml6 vcrun2005 vcrun2008 ie6 fontsmooth=rgb

5. Install Adobe Photoshop 6

$ cd /home/user/path/to/installer

$ wine Set-up.exe

From here and on, the installation process will be the same as when you install Adobe Photoshop 6 on Windows.

Enjoy!