iPhone 12 / Instagram Menu Bar

Hi, I have just set up my new iPhone 12 and installed all the apps.

One issue: when I use Instagram, when I scroll down on the main page, the menu bar icons disappears (add post, likes and messenger). How can I fix this issue? The menu bar should be here permanently when I scroll down. I've already tried to delete the app, re-install it...turn off my phone...everything... I have the same issue with Facebook.

Thanks for your help

Jade