How do you make a GIF with multiple images?

The response from @Imaginerie is good because it helped me realize that the solution for what's being asked is actually a two-step process. First, you need to use Adobe Express to make a video from multiple images. Then you need to use Adobe Express to make a GIF from that video.

A helpful YouTuber named Mesha Daniel has brief demos of each of these steps:

Create Video from Images in Adobe Express
https://www.youtube.com/watch?v=stmtZAGH45I

Create GIF from Video in Adobe Express
https://www.youtube.com/watch?v=dZf0cjTpxK8

The best way to do it in Adobe express would be to make a regular video (so compile your scenes, make your transitions, animations etc) and export as PM4. Once you got your MP4, go to the quick actions and choose "convert to Gif"

a few caveats:
Gif is an old format. It only accpets a limited amount of colours and size.
Keep it very small. (I think the maximum should be 1500 px wide)
keep it short
Be prepared to have the quality degraded compared to your MP4 (that's what GIF does)
You have more options to tweak the quality in pro software like Photoshop, but you can still do it in Adobe Express.

For info: Here are the recommendations for uploading on Giphy, which is the platform that hosts GIF for the majority of social media (if not all)
https://support.giphy.com/hc/en-us/articles/360019914771-GIF-Creation-Best-Practices