GIF and animated WebP
Export › GIF & Animated WebP makes an animated picture for places that don't play SVG or video: email, chat apps, documents. The preview is made from the real file each time you change a setting, so the size you see is the size you get.
Step by step
Open Export, pick GIF
Click Export in the top bar, then GIF & Animated WebP across the top of the window. File is GIF, which plays everywhere, with at most 256 colors per frame; Animated WebP has every color and is much smaller, but most email apps don't show it.
Choose its size
Under Size, Scale is 75% of the document. Click 50%: the line above the preview shows the new file's size, and how much smaller it is than a plain GIF of the same frames.
Use fewer colors
Under Compression, drag Colors down from 128: fewer colors, a smaller file. Keep exact keeps the colors you tick (a logo's, say) exactly, and Dithering mixes dots of the colors there are, so gradients don't band.
Compare with the original
The preview shows the frame at the playhead twice: the original on the left, the GIF on the right. Drag the divider to compare them.
Play the file
Click Play under the preview: it plays the file itself.
Download it
Click Download .gif at the bottom right. Embed in your site has the code for your page; tick Also an Animated WebP there and Download the set (.zip) makes both, the WebP for browsers with the GIF behind it.