Animated WhatsApp stickers are just short looping WebP files. If you already have a GIF or a clip from your camera roll, you do not need a separate animation app.
Limits that actually matter
WhatsApp caps animated stickers at roughly 6 seconds and 512 KB. Longer videos get trimmed and compressed here so the sticker still sends.
GIF vs video
GIFs are already looping, so they convert cleanly. MP4, WEBM and MOV work too — pick a clip where the motion is obvious in the first second, because that is what people see in the tray.
When to use a static sticker instead
Memes with small text, portraits and logos often look sharper as static stickers. For jokes and reactions, animation wins. You can make both with the same sticker maker.