Thanks for feedback. Sorry for any misleading.
Unfortunately, there isn’t such workflow. This is just the browser’s option that allows you to save the downloaded file into your Photos app. Let me provide some insights.
When you open your Bubble web app and hit to download the gif image (in case you’re on Safari), it opens it in a new tab and you’re able to save it to your Photos, here:
Also, make sure that your browser allows to save it. You can go to Settings → screen time → content & privacy restrictions → photos → allow to check on it.
Hope it helps.