Hello erik14,
Thank you for using Apple Support Communities. You might be able to check the Messages settings to see if the option to remove GIFs is listed. Go ahead and follow the steps below:
1.) Navigate to Settings > Messages.
2.) Tap on iMessage Apps.
In this section you will see a list of apps that work with iMessages. You'll be able to remove or turn off apps that provide GIFs. Also, this resource doesn't have any details related to disabling GIFs in general: Send and save GIFs on your iPhone, iPad, or iPod touch - Apple Support
Because of this, you might have to provide Apple feedback. If you'd like to provide feedback on your experience with Apple products or services, you can do so using this link: Legal - Unsolicited Idea Submission Policy - Apple
Thank you for using Apple Support Communities. Take care.