Overview
I made these shop, inventory, settings, and invite-friends systems for a client a few years ago.
Complete Showcase:
Below are the main buttons for each UI system. I made sure to add adequate animations and sound effects to all of the UI elements.

Settings
The only settings option my client asked for was a "Favorite Color" option which would be used to change the colour of all of the game's GUI.

Inventory
For the inventory, my client asked me to create 6 categories but set up only 2: Tools and Clothing.
This shows only the items that are owned by the player and allows the player to equip or unequip the respective items. The items that are equipped and unequipped are pointed out with green and red "Equipped"/"Unequipped" text, respectively.

Similarly, the same works for the clothing category where the player can see all their owned clothing and mix and match, wearing their choice from the list. The clothes that the user chooses to wear are highlighted in green.

Here's the avatar once the user has finished customizing it:

Shop
Again, for the shop, my client asked me to set up 2 of the 6 categories with tools and clothing.
The item list shows each item with a description and price. Clicking on any item will prompt a purchase. Owned items are marked with a ✅ checkmark and text saying, "Owned".

The clothing category in the shop allows users to filter the clothing by type. Clicking on any piece of clothing will prompt the user to either try on the piece for 5 seconds or buy it.

This is how the prompt looks:

Invite Friends
This system allows users to invite any of their friends to the game with a simple message.

Players can either scroll through their friends list or search for a specific friend they'd like to invite.

Conclusion
Overall, working on this project was a great experience. I remember, I'd to go out of city while this project was active, so I worked at night on a laptop on vacation. Unfortunately enough, the client ended up scamming me and I never received the payment for this project. Since then, I've upped my security game.