How to disable gifs from playing on Discord Mobile for Android
For a while you couldn't do this and now you can!
Step 1: navigate over to your User Settings by clicking the small version of your avatar at the bottom of the screen
[ID: a screenshot of discord's user settings, labeled thus at the top, with an avatar below, a username (blacked out) and a list of settings. The first heading is 'User Settings' and includes 'Set Status', 'My Account', 'Privacy & Safety', 'Authorized Apps', 'Connections', and 'Scan QR Code'. The next heading is 'Nitro Settings' and is cut off. At the bottom of the screen are a number of icons, from left to right: the discord icon, a person waving, a search icon, an 'at' (@) symbol, and another user avatar, circles by me in red. End ID]
Step 2: Scroll down to Accessibility, under App Settings
[Image ID: The user settings screen but scrolled down. There is a heading 'App Settings' which includes 'Voice and Video', 'Notifications', 'Text and Images', 'Appearance', 'Accessibility', 'Behaviour', 'Language', and 'Activity Status'. 'Accessibility' is highlighted in yellow and has a yellow arrow drawn by me pointing to it. End ID]
Step 3: Toggle off 'Automatically play gifs when possible'
[Image ID: The accessibility menu. The first setting is Reduced Motion, that has a description: 'Reduce the amount or intensity of animations, hover effects, and other moving effects across Discord. Need help? Check out our Help Center for for info!' It is followed by a toggle switch labeled 'Enable Reduced Motion'. The other settings are 'Automatically Play gifs when possible', 'Play Animated Emoji' ('I want Emoji to move and groove'), and three options for animating stickers 'Always Animate', 'Animate on Interaction' ("On the desktop client, stickers will animate on hover or focus. On mobile client, stickers will animate on long-press.") and 'Never Animate'. The 'Automatically play GIFs when possible' is highlighted in yellow, and the on-off slider has a drawn yellow arrow pointing to it. End ID]
Some of the other settings under accessibility can also be helpful to reduce annoying auto-playing movement.
And a reminder this is for Android mobile, I don't know how IOS works.