Create / Edit KeyPad

In the main screen tap on the ⚙️ icon, and select "Edit KeyPads"

You can change keypad layout to fit your needs.
Tap ➕ or 🗑 buttons in the toolbar to add and remove rows or columns of buttons.

Enter editing mode by tapping Edit button in the top right corner if you want to merge multiple buttons into one,
or split one big button into multiple independent buttons. Select buttons by tapping them while in editing mode, and then use ⊞ button in the toolbar.

Tap on any ➕ key to assign to it key combination,
or enter editing mode to edit its title & icon.

To assign a key its keyboard combination, tap on the keyboard keys on the screen.
You can assign multiple shortcuts to one key, by inserting separator between them (top right corner just above the keyboard).
By default separator will not introduce any delay between the shortcuts (0 ms), but you can change that by tapping it in the preview area.

You can also tap keys in the preview area to remove them from the shortcut.
Keyboard shortcuts can consist from multiple modifier keys and one regular key.
Possible modifier keys are: ⌘ Command, ⌃ Control, ⌥ Option, ⇧ Shift.