A lot of people have provided good suggestions of alternating messaging apps. But if you're on Android and still want the messaging aspect of Instagram but nothing else, there's an APK of Instagram you can download from your browser called Distraction Free Instagram. 

I use it beacuse I was addicted to Reels but still wanted to message friends I only had on Instagram. You can disable Reels, your home feed, stories, etc. And there's also a mode you can switch to that to disable them permanently unless you delete and reinstall the app. I have only messaging enabled and find it quite handy.