Krita is the full-featured digital art studio. It works well on the RPi4 8 GB model.

It is perfect for sketching and painting, and presents an end–to–end solution for creating digital painting files from scratch by masters.
Krita is a great choice for creating concept art, comics, textures for rendering and matte paintings. Krita supports many colorspaces like RGB and CMYK at 8 and 16 bits integer channels, as well as 16 and 32 bits floating point channels.
Have fun painting with the advanced brush engines, amazing filters and many handy features that make Krita enormously productive. https://krita.org/en/
First, you need to install Flatpak. A flatpak package is available in Raspberry Pi OS. To install it, run the following as root:
sudo apt install flatpak
Next, add the Flathub repository. Flathub is the best place to get Flatpak apps. To enable it, run:
flatpak remote-add –if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
Reboot your PI.
To install Krita, run the following as root:
flatpak install flathub org.kde.krita
Once installed, to run Krita type the following command:
flatpak run org.kde.krita
That’s it! You should now be able to run the Photoshop like program on your Raspberry Pi 4.