There are many websites that claim to have fixes for when Teams gies not display GIFS. The GIF icon was not displayed in my Windows Program but was displayed in the browser and the mobile app.
None of the fixes worked for me except the following:
In Settings (...) at the top of the Teams client > Privacy , Scroll down to Optional Connected Experiences and turn it on. If it is turned off, it will turn Giphy off and you will not be able to use GIF's
